British Prime Minister Theresa May's final bid to salvage her EU divorce deal appeared doomed as pro-Brexit Conservatives and the opposition Labour Party rejected her attempts at compromise.

Brexit Party leader Nigel Farage (C) holds up a placard at the end of a European Parliament election campaign rally at Olympia London, west London on May 21, 2019. (Photo: AFP)

May is likely to face an intense session at Prime Minister's Questions in parliament Wednesday, a day before Britain votes in EU elections it had not expected to take part in three years after the Brexit referendum.

The embattled leader Tuesday promised to give lawmakers a vote on holding a second Brexit referendum and dangled a package of sweeteners she hoped could resolve the Brexit crisis.

MPs have already rejected her Brexit deal three times.

May has already said she will leave office shortly after the measures she outlined are put up for a vote early next month -- no matter the outcome.

In her televised address Tuesday, she promised to give lawmakers a chance to set a confirmatory referendum on whatever version of Brexit they end up approving in the weeks or months to come.

"I recognise the genuine and sincere strength of feeling across the house on this important issue," May said.

The measure is a key demand of the main opposition Labour Party but is bitterly opposed by Brexit-supporting Conservatives whose votes May also needs if she is to get her deal passed.