Former Prime Minister Boris Johnson flew to Venezuela last month for a private meeting with the country’s President Nicolás Maduro.
The talks were unofficial and not paid for by the UK government, the BBC has been told.
Mr Johnson’s spokesman said it was to «emphasise the need for Venezuela to embrace a proper democratic process».
The Sunday Times first reported that Mr Johnson travelled there by private jet while on holiday in the Caribbean.
It is not clear who initiated or paid for the visit.
Mr Maduro has ruled Venezuela since 2013. He faced widespread protests but in 2018, won a second term in presidential elections that were widely dismissed as neither free nor fair.
The UK has an embassy in the country but no ambassador, though it does have a charge d’affaires, Colin Dick.
A spokesman for Mr Johnson told the BBC that he «repeatedly made clear there can be no hope of normalisation in relations until Venezuela fully embraces democracy and respects the territorial integrity of its neighbours».
«He also set out the case for the cause of Ukrainian victory to the government of Venezuela.»
A spokesman for Foreign Secretary Lord Cameron said it was a «private visit» but that Mr Johnson texted him when he was on his way.
Mr Johnson’s office declined to say who paid for the private jet that flew him to Venezuela, saying: «Now that he is a private citizen we don’t comment on any of those issues, only to say there was no cost to the UK taxpayer nor the Venezuelan government».
The BBC has been told that Mr Johnson received a briefing in the British Embassy residence in Caracas before his meeting, and that he then debriefed embassy officials afterwards.
The visit is unusual given the former prime minister is not a member of the government anymore, and because of the current diplomatic tensions between the UK and Venezuela.
Venezuela’s government faces strong international pressure to hold a free and fair election, to release activists and political opponents it has detained, and to de-escalate tensions with its neighbour – the former British colony Guyana.
Venezuela held a referendum last year in which it claimed sovereignty over the oil and resource-rich Essequibo region that makes up about two-thirds of Guyana, a claim that Guyana disputes.
The UK sent a warship to Guyana in response to show military and diplomatic support for the country. Mr Maduro called it an «act of hostile provocation».
Venezuela has announced it will hold presidential elections on 28 July where the incumbent president is expected to stand. The UK, along with the US, the EU and Canada all want to see a restoration of democracy.
A deal was reached last year with the opposition to allow a free and fair election to take place, with international observers present, but since then a ban against the opposition leader has been upheld.
This led to the US reimposing some of its economic sanctions on the country.
Last year, Mr Johnson, who had left his post in Downing Street in September 2022, made an unannounced visit to the Ukrainian capital Kyiv where he met President Volodymyr Zelensky.
Mr Johnson then stepped down as MP in June 2023 after facing some criticism over how many parliamentary votes he was missing because he was making frequent trips abroad.
Then in November 2023, he was pictured alongside former Australian Prime Minister Scott Morrison in Israel where they met the country’s president, four weeks after Hamas’s attacks on Israel on 7 October.
He returned to Kyiv last month after his Caribbean holiday to meet Mr Zelesnky on the second anniversary of the Russian invasion.