British Prime Minister Theresa May is set to become the first leader to visit US President Donald Trump since his inauguration.

Mrs May and Mr Trump will spend about an hour in face-to-face talks later today in the Oval Office.

The main topics of conversation are expected to be Britain's hopes of a free trade deal following Brexit and the two countries' shared security concerns.

Speaking to reporters on her flight to the US, ahead of a speech to leading Republicans in Philadelphia, Mrs May said President Trump shared some of her political values, and that of Brexit Britain.

She said: "I think we both share a desire to ensure that governments work for everyone and particularly that governments are working for ordinary working class families.

"I think that's important. That's what I've spoken about.

"I did it on steps of Downing Street when I became Prime Minister; a country that works for everyone and an economy that works for everyone.

"I think we share that interest and that intention in both our countries."

The meeting comes a day after Mrs May spoke to congressional Republicans at their retreat in Philadelphia.

In her speech, she warned there can be no return to Iraq-style intervention in other countries by the US and UK.

But she cautioned over foreign policy positions taken by Mr Trump during his campaign, warning that he should "engage but beware" of Vladimir Putin and Russia and underscoring the work of the UN as "in need of reform, but vital, still".