Rail firms came under fire this weekend for planning a series of fare hikes of up to 87 per cent just ten days after the general election - despite the main party leaders pledging to freeze prices . The Prime Minister has requested First Great Western ( FGW ) 'urgently review ' its decision to almost double some fares on the route between London and the Cotswolds - which passes through his Witney constituency . Mr Cameron has promised to freeze fares in real terms for the whole of the next parliament , while Labour has also pledged to bring in a 'cap ' on price hikes . Scroll down for video . Sent letter : Prime Minister David Cameron has written to First Great Western to request it 'urgently reviews ' plans to increase fares on trains running through his Witney constituency . Passengers travelling from Charlbury , the Oxfordshire station nearest to his constituency home , can currently purchase an off-peak return to London costing £33.30 . This allows them to leave at 9.42am , outside the morning peak , but return on one of the four services that go from London during the evening peak period . But from May 17 , these customers will be forced to pay £62.40 if they want to come home on one of these trains - an 87 per cent increase . The planned changes have angered Mr Cameron 's constituents - prompting him to personally intervene . 1 . First Great Western . Line : London to Hereford . Potential increase : 87 % . 2 . Virgin . Line : Stafford to Liverpool . Potential increase : 24.5 % . 3 . London Midlands . Line : Crewe to Northampton . Potential increase : 23 % . The Prime Minister 's spokesman told The Sunday Times : 'Mr Cameron has written to First Great Western and asked them to urgently review their decision . ' Train companies have three windows every year in which they can increase 'unregulated ' fares , which make up around half of their total revenue . Unregulated fares can include journeys such as off-peak leisure and advance-purchase tickets . First Great Western has insisted the reason for the change is to bring the north Cotswolds route in line with its other services . The firm is also offering some customers a cheaper option in advanced single tickets , potentially allowing them to buy a return for £20 if they book ahead . Other sharp price hikes to be introduced include an off-peak first-class single from Crewe to Northampton on London Midlands , which will rise from £30 to £37 , according to trainsplit.com - a website that provides passengers with cheaper ticket options . The cost of an anytime return between Stafford and Liverpool , travelling with Virgin , will leap from £26.50 to £33 - a 24.5 per cent hike . Biggest hike : Passengers travelling with the rail firm between London and the Cotswolds could face increases of up to 87 per cent come May 17 . And an anytime first-class day return on Virgin from Manchester to Stoke will go up 22 per cent - rising from £29 to £35.30 . Virgin has said the 'vast majority ' of its price hikes affected 'Virgin Trains-only fares ' - which are at least 20 per cent cheaper than tickets offered by rival firms . It added : 'Our overall fare increase this year on the west coast is just 1.65 per cent , well below the industry average . ' Speaking to Mark Hookham of The Sunday Times , Mike Richardson , of trainsplit.com , said : 'Passengers might very well be surprised at these fare increases when both the main parties have talked about price freeezes . According to Which ? Hundreds of 'anytime ' and 'off-peak ' returns rose by 40 per cent in January . Its research found rail fare increases on tickets that passengers buy on the day and on rural routes . Defended rise : Virgin has said the 'vast majority ' of its price hikes affected 'Virgin Trains-only fares ' - which are at least 20 per cent cheaper than tickets offered by rival firms .
PM has written to First Great Western asking for 'urgent review ' of fare hike . The letter says the company is "concerned that passengers may be adversely affected by a change in fares and we would like your immediate attention on this matter."