Provided that if either—

1. (a) the undertakers; or
2. (b) such number of consumers not less than twenty as the Minister of Transport considers sufficient having regard to the population of the area of supply; or
3. (c) in a case where the local authority are not themselves the undertakers, the local authority; or
4. (d) in a case where the local authority are not themselves the undertakers and the area of supply is situate wholly or partly within the county of London, the London County Council,

at any time after the expiration of three years after the confirmation of the special order make a representation to the Minister that the prices or methods of charge stated in the special Order or approved by the Minister ought to be altered, the Minister, after such inquiry as he may think fit, may make an Order varying the prices or methods of charge stated in the special Order or so approved as aforesaid, or substituting other prices or methods of charge in lieu thereof, and the prices or methods of charge so varied or substituted shall have effect on and after such day as may be mentioned in the Order as if they had been stated in the special Order: