GMB leader Paul Kenny blasted Blairite “nostalgia” for New Labour yesterday as he urged leadership candidates not to take the party back two decades.

Mr Kenny, chair of the Unions Together group that represents Labour’s 14 affiliates, said Labour returning to the politics of a “bygone age” would not help it win the 2020 election.

He said: “If the Labour Party acts in haste it will repent at leisure.

“Any attempt to reintroduce a quick fix based on nostalgia and a view of the world as it was nearly a quarter of century ago would lead to catastrophe or disaster.”

Mr Kenny also issued a stinging response to Peter Mandelson’s calls for the unions to be frozen out of Labour’s future.

The arch-Blairite claimed on Sunday that Labour had an “unhealthy” relationship with trade unions that “was not a good look” to voters.

He said the party lost the election because Ed Miliband made a “terrible mistake” by breaking with New Labour and turning left.

But Mr Kenny hit back: “The absurd anti-union remarks made by Lord Mandelson will do nothing but reignite divisions that are completely and totally unconnected to the reasons why Labour lost the election last week.”

The GMB leader also used his post-election statement to call on the labour movement to face up to “fundamental problems” with the EU.

“Whatever the European vision was on integration, harmony, economic advancement and political stability, what we currently have isn’t it,” he said.

“Right-wing governments and employers have engineered massive change in the direction of the EU vision.”

He also predicted that “many organisations traditionally in favour will campaign for a No vote” in the forthcoming EU referendum.