British lawmakers ­gathered  on Monday to honor their ­murdered colleague Jo Cox, ­attempting a rare show of unity in the midst of a heated, neck-and-neck race for votes three days before a referendum on whether to quit the EU.

As the battle raged over Thursday's vote, which could change the course of postwar Europe, the latest polls showed the "Remain" camp gaining ground.

Politicians from both sides of the fight returned to Parliament - which had been in recess - to pay tribute to Jo Cox, a Labour Party MP who campaigned in favor of EU membership and who was shot and killed last week in a village street in northern England.

Her alleged killer, 52-year-old Thomas Mair, was due in court on Monday after being charged with murder over the weekend.

The image of unity did not last long.

Top pro-Brexit campaigner Nigel Farage, the leader of the UK Independence Party, ­accused his rivals of unashamedly using Cox's death to boost their cause.

"The 'Remain' camp are using these awful circumstances to try to say that the motives of one deranged, dangerous individual were similar of half the country, or perhaps more, who believe we should leave the EU," he told the BBC.

While the "Remain" camp has tried to focus on the potential economic damage that Brexit could inflict, the "Leave" campaign has held out the promise of Britain taking better control of rising immigration if it leaves the EU.

Farage, however, has had to fend off attacks over his release last week of a campaign poster showing scores of refugees trudging through fields toward the camera with the bold, red headline, "Breaking Point."

Former Conservatives Party chair Sayeeda Warsi, a senior member of British Prime Minister David Cameron's ruling party, announced she was withdrawing support for "Leave" ­because of the poster.

The "Leave" and "Remain" sides have now battled each other to a virtual stalemate, with each receiving exactly 50 percent of popular support, according to an average of the last six polls as calculated by research site What UK Thinks.

Both sides agree that the stakes are high.

Foreign Secretary Philip Hammond, arriving for a meeting with EU counterparts in Luxembourg, warned that a British vote to leave the EU would be "irreversible."

If Britain leaves the EU, it would be the first nation to do so in the bloc's 60-year ­history.