An advocate-general of the European Court of Justice ruled the Government broke EU equality rules by denying men cut-price passes until the age of 65, while women qualify at 60.
The interim ruling - certain to be upheld by the full court in the summer - opens the floodgates to refund claims from thousands of men and will be seized upon by Euro-sceptics as another costly interference in Britain's right to make its own laws. There are an estimated 1.5 million men aged 60 to 64.
It comes only six months after a similar judgment which forced the Government to give free prescriptions to men at 60 - the same age as for women -and at a cost of pounds 40m a year. Ministers had the choice of raising women's age of entitlement to 65 but decided not to risk the electoral unpopularity.
The Government had already made provision to equalise the retirement age at 65 for men and women between 2010 and 2020, and the prescription age will go up at the same time.
The pensioner who brought the test case, Stanley Atkins, a retired garage mechanic from Ketley Bank, Shropshire, said: "This is an important step along the road to putting right a major injustice."
His victory was welcomed by campaigners for the elderly. Sally Greengross, director general of Age Concern said: "Public transport is vital to older people's freedom and independence. Age Concern would like to see the introduction of a national concession scheme for all those over the age of 60.Reuse content