The present European Parliamentary Labour Party is as much a fortress of the Blairite Resistance as is the Labour Party's paid staff, especially in London, though also elsewhere. But Blair once purged about three quarters of Labour MEPs in one go. It can be done.
But I could never vote for him, I never have voted for him, I have therefore never voted Labour in a European Election, and I do not know why the Labour Party, as such, continues to put up with him. For 20 years, I have been listening to him tell audiences that he wanted national institutions to disappear completely, leaving only European and regional ones. That bears absolutely no resemblance to Labour Party policy, nor has it ever done so.
Through gritted teeth, I have instead voted for the SLP (it and I were both that young, although its very young and solidly Catholic present President is well worth watching)), for Respect, and then for No2EU - Yes to Democracy. A bit more happily in the last case, but it too has since become TUSC, just another competitor for the tiny sectarian Leftist vote.