A new fast train service between Milton Keynes and London has been blocked by the Office of Rail Regulation.
The Great North Western trains planned to use new tilting Pendolino trains to give passengers greater choice.
The scheme was given the green light last summer, but rejected over Christmas by the rail regulators.
ORR considered the new service failed their NPA (‘mot particularly abstractive’) criteria.
The decision has been blasted by Labour parliamentary candidate Andrew Pakes.
He claims regulators were worried the new trains would divert profits from West Coast Mainline franchise holder Virgin and undermine the income Virgin could pay to the government.
Mr Pakes said: “This is a deeply worrying decision by the ORR that means Milton Keynes will lose out on new rail services.
“The price of a season ticket from MK to Euston has rocketed by over £1,000 since 2010 with little choice for passengers. There is something clearly wrong when the regulator puts the profits of existing train companies ahead of better services for passengers.”