Jay Lee, 34, from Bexley, south-east London, was thrown out of Aslef when the union made the discovery.

Mr Lee, who stood as a candidate for the far right group, had complained to an employment tribunal about his removal two years ago and won.

A new hearing will take place after the Employment Appeals Tribunal's decision.

Union 'vindicated'

Aslef says it believes it has been vindicated for the expulsion and has a "very strong case".

Shaun Brady, general secretary of Aslef, said: "This ruling vindicates Aslef's actions.

"We have no place in our union for racist views, and we will seek to expel members who promulgate these unrepresentative attitudes.

"Train drivers work in a multiracial environment and as their union we wish to reflect the community that we serve. "