Police in the UK are investigating allegations that someone has issued death threats against prominent Brexit supporters, including the senior Conservative Party politician and Leader of the House of Commons, Andrea Leadsom.

The threats were sent anonymously by an individual or group that signed itself "the real 48 percent". The Times newspaper reported the typed letters had been addressed by hand.

"The real 48 percent" alludes to the referendum vote held in the United Kingdom in June 2016 in which 51.9 percent of those who voted indicated they wanted the UK to leave the European Union. The Guardian newspaper said the sender appears to be someone who wants the UK to remain within the EU.

Britain has been divided since the referendum 19 months ago and the debate has raged about whether the vote should have been held, whether the decision was the right one, and whether the UK should completely sever its ties with the EU, or maintain a close relationship.

The Guardian reported that four death-threat letters have been passed to police, two on Friday and two on Monday. The Evening Standard newspaper added that the recipients were all MPs who strongly supported the Brexit campaign. The identities of the other MPs have not been confirmed by police.

Additionally, the Guido Fawkes website reported last week that six prominent donors who financially supported the campaign to leave the EU had received similar letters.

The Sun newspaper said the people who sent them are believed to have used an online list of Brexit donors to identify targets.

Leadsom posted a photograph on Twitter of the letter she received.

It included the sentences: "You have taken lives on our side. Now we will take lives on yours. We are coming for you."

She said on Twitter the sender was a coward for writing anonymously and described the act as "pretty despicable".

Sky News said the Metropolitan Police had confirmed that officers are probing the alleged death threats.

Last week, British Prime Minister Theresa May said abuse in public life was a major problem that threatened democracy.