Most people in south Wiltshire are very proud of the achievements of both establishments at Porton Down: the Centre for Emergency Preparedness and Response, and the Defence Science and Technology Laboratory. If they did not exist, they would have to be invented. In the fevered minds of journalists, they are shadowy and mysterious homes of the dark arts, and likely to generate extravagant language, but to most local people the reality is very different. We know that the work of all involved, from the scientists of international repute to the staff who keep the place going, is vital to our national interest and well-being.

It all started in 1915 when chemical weapons were first used against British troops. The carnage was appalling. In 1916, work started on anti-gas defence and respirator development, as well as research on how chlorine, mustard gas and phosgene were disseminated. Porton Down was chosen because it is an isolated, 7,000 acre site with very little human habitation downwind for many miles.

By 1956, the United Kingdom had abandoned any sort of chemical and biological warfare capability and restricted work to hazard assessment and defence. In 1979, the Government split off the Ministry of Defence Porton Down biology department to the Department of Health, which established the Centre for Applied Microbiology and Research, which is now part of the Health Protection Agency and known as the Centre for Emergency Preparedness and Response. However, the two establishments, which are treated as one by the Health and Safety Executive, work together, adding resilience to both. That relationship should not be broken.

Dangerous pathogens of humans, animals and plants are a major threat to public health and the nation's economy. At Porton Down, research is done to understand dangerous pathogens, and how to detect and treat them. Pathogens evolve constantly, so we must always be one step ahead-some 38 new species of human pathogen have been found in the past 25 years. Climate change will affect the emergence and characteristics of infectious diseases, and their transmission in the UK. Globalisation and the ease of international travel allow infections to spread rapidly.

Dangerous pathogens can be weaponised and the security services are alert to the potential for the malicious use of pathogenic material as a terrorist weapon. Anthrax was used as a weapon in the USA in 2001. Porton Down has always been a world leader in that work, as I discovered when visiting the US Centres for Disease Control and Prevention in Atlanta, Georgia, and the US Government's Lawrence Livermore Laboratory in California. Indeed, the US Government have invested in HPA Porton Down and currently commission work there.

The HPA has been at the forefront of tackling every biological problem in the past 25 years. In 1986, bovine spongiform encephalopathy was identified, and later the human variant Creutzfeldt-Jakob disease. In 2001, more than 6 million animals were destroyed in response to foot and mouth disease. Swine flu put HPA Porton Down under pressure in terms of public health planning, anti-viral stockpiling and accelerated vaccine manufacture.

Smallpox, Ebola, anthrax, plague, botulinum, clostridium difficile, ricin, West Nile disease, swine flu and other pathogens that are continually evolving and changing are all in a day's work at the centre. They are the most deadly pathogens in the world. I salute the scientific work force and their supporters whose research, developments and trials at Porton Down help to protect our nation every single day and prepare us for the worst, whether natural or man-made. Also manufactured at Porton Down is life-saving Erwinase, used to treat leukaemia, the most common childhood cancer, saving some 1,400 young lives every year.

All Governments have recognised the growing importance of this work. In 2008, the Government announced a major multi-million pound rebuilding programme to give the HPA state-of-the-art, world-class high-containment laboratories to levels CL3 and CL4. They would take full advantage of the highly specialised science community at Porton Down and rebuild on the 85-acre North Field site. The high-level security of the site, co-located with the Ministry of Defence laboratories, is ideal. This redevelopment is known as the Chrysalis programme.

The local community is supportive. Indeed, generations of scientists are the local community, and their presence has seen the development of exceptionally large and successful science departments in local schools. Wiltshire council is proactive in providing infrastructure and community services as well readily granting planning permission and promoting the emerging Porton science park. In September 2009, the chief executive of the HPA wrote to me saying:

"We continue to be on track to finalise and submit the Outline Business Case for the project in Spring 2010".

In October 2009, out of the blue, someone mentioned Terlings Park in Harlow, and the possible conversion of a mothballed 30-year-old pharmaceutical plant, as an alternative to the on-site rebuild, on which the HPA had already spent £10 million. Last month, Terlings Park became the HPA board's favoured location. This about-turn was met with shocked disbelief by the work force at Porton Down. Both management and trade unions, on behalf of the whole work force, have made the argument against such a misconceived move. HPA management claims that the short-term risks of disruption and hiatus will be outweighed by the 50-year, long-term advantages of synergy with other HPA sites not very far from Harlow. We do not know how they arrived at that conclusion because they have refused to allow us to see the two key documents, their consultants' reports on the outline business cases and the preferred options analysis. I ask the Minister when those documents will be available for public scrutiny.

I put it to the Minister that a number of points are clear, and they do not support the proposed move to Harlow. The main argument of HPA is that Porton Down is a long way from the other sites-the Radiation Protection Division and Chemical Hazards and Poisons Division at Chilton, Oxfordshire; the Centre for Infections at Colindale in London; and the National Institute for Biological Standards and Controls at Potters Bar. If CEPR moved closer to the other three, HPA alleges that over 50 years a synergy would develop that would outweigh the short-term risks.

So what are the risks? Terlings Park cannot accommodate all the CEPR activities and there is no room for growth, whereas all the other sites could move to Porton Down tomorrow with room to spare. The close working relationship with the military side of Porton Down would be lost and so would their joint resilience. If CEPR is moved to Harlow, it will in fact disintegrate. All the years of expertise in safe handling of the most dangerous organisms in the world will be lost, as will the animal modelling and translation on interventions. The move would also undermine Porton Down's external income-generating capacity, which currently covers more than two thirds of the costs of running CEPR every year.

Most of the scientists have roots in the Salisbury community and do not wish to move to Harlow. Many of them work on programmes funded by the US National Institute of Allergies and Infectious Diseases, which has supplied most of the investment necessary. Would it stand by and watch CEPR walk away to Essex? Would it fund its investment all over again? The risk is too high.

The physical security of the Porton Down campus infrastructure bears no comparison to the Harlow site, which would be very vulnerable. The introduction of dangerous pathogens to the Harlow urban environment is high risk and I do wonder whether the good people of Harlow would really wish their council to agree to it. Inevitably, animals used in trials, including primates, would have to travel by road from Porton Down to Harlow, where safe animal accommodation would have to be provided to support the biological investigation services. Would that be acceptable to the citizens of Harlow?

The Minister confirmed in a parliamentary answer, on 22 February, that the CEPR has been working since 2005 to provide advice and expertise to the organisers of the Olympic and Paralympic games in London in 2012. Any incident during the Olympic games would occur at a time of maximum disruption to the Porton Down CEPR, if it were on the move to Harlow.

The proposed move of 800 Government employees to Harlow in the crowded south-east of England is exactly contrary to the Lyons review, which said that public employees should be moved out of the south-east. Such a move would also be contrary to the report of Sir David Cooksey, which concluded that too much of our excellent medical research failed to translate basic and clinical research into ideas and projects and thence into clinical practice. But that is exactly what happens now at Porton Down-a national benefit that risks being destroyed if CEPR is broken up and sent to Harlow.

I appeal to the board of the Health Protection Agency, the members of which are all extremely distinguished scientists-one has extensive commercial experience in the pharmaceutical industry-to ask itself if it really, in its heart of hearts, supports this disruptive and risky gamble, which would destroy 94 years of scientific excellence that is admired and respected all around the world, and which has a great future at Porton Down.

I have written to the permanent secretary at the Department of Health, saying that I am alarmed by the haste with which the board is seeking a ministerial decision so close to a general election, and asking him not to agree to such a request being made to the Minister. But if it is, on behalf of my constituents, I ask her to consider the wider implications for national security as well as the impact on the work force at Porton Down and the wider community of Salisbury and south Wiltshire, before she makes a decision of such magnitude.