Former British prime minister John Major has called on Theresa May to cancel or postpone Brexit "with immediate effect", saying the "chaos" in the UK cannot be welcomed by anyone.

Mr Major, who served as British prime minister in the early 1990s, said Britain needs more time to address the stand-off in the country just months out from the March 29 Brexit divorce date.

Speaking at a specially arranged Institute of International and European Affairs event at the Westin Hotel in Dublin, Mr Major repeatedly hit out at the rise of "ugly nationalism" in Britain and other countries.

Urging Theresa May to pull back from the brink before it is too late, he said article 50 should be cancelled "with immediate effect".

Whether you are a remainer or a leaver, no one can welcome chaos.

"it is time to turn to reality, not fiction. Facts, not ideology. We now need to revoke article 50 with immediate effect.

We now need the most precious commodity of all: time," Mr Major said.

The former prime minister also used his speech to criticise how" selfish nationalism is on the march" and the rise of "ugly intolerable nationalism", xenophobia and "strongmen" worldwide.

Noting the "disconnect in logic" from staunch Brexiteers who claim Britain is strong and can "go it alone'" yet also claim it is weak and being bullied by EU bureaucrats, he said:

They must decide if we are the United Kingdom or Little England... They say the EU damages us.

"Well, the UK has shown we are perfectly able to inflict damage on ourselves, without any help from the EU."

Raising the risk of a hard border on the island of Ireland if Brexit falls off a no deal cliff edge, Mr Major said such a situation would "re-awaken the worst of days" and would create a physical and pyschological split of "them and us".

Finishing his speech, Mr Major repeated it would be his "preference" to revoke rather than delay article 50, adding:

"We can do this, we should do this, and we must do this."