The UK was supposed to exit the EU on March 29 after the majority of the public voted leave in the 2016 referendum. But following a humiliating defeat in the Commons over the deal she had negotiated with Brussels for two years, Mrs May was forced to ask EU leaders for an extension. Now the UK is scheduled to leave on October 31 instead.
A no-confidence vote by grassroots Tories next month will not be binding, but will add pressure on the Prime Minister to quit if it is passed.
Mrs May won a previous confidence vote of MPs in December, which means she cannot be officially ousted for a year.
But over the last week, attempts were made to try and change the rules.
The aim was to stop her having 12 months before any further confidence motion can be put forward.
Mrs May previously said she will resign if her withdrawal agreement is voted through.
She also faced further defeats in the recent local elections after the Conservatives lost more than 1,300 councillors across the UK.
As Mrs May struggles to cling on as Prime Minister, we are taking a look back at the 15 leaders of the UK since 1945.
Clement Attlee (Labour, 1945-1951)
Mr Attlee overhauled social services and the public sector in post-war Britain, as he created the National Health Service (NHS).
He also nationalised huge industries and played a massive part in decolonising India, Pakistan, Burma, Ceylon and Jordan, along with seeing the state of Israel being created after the UK withdrew from Palestine.
Winston Churchill (Conservative, 1951-1955)
The iconic leader served as Prime Minister twice and helped lead the UK to victory in World War II.
He also raised the age of school leavers to 14-years-old an introduced the 11+ exams.
Mr Churchill was also awarded the Nobel Prize for Literature in 1953 for his many published works.
Anthony Eden (Conservative, 1955-1957)
Mr Eden worked in the Foreign Office and was Foreign Secretary three times during World War II and the Cold War.
After becoming Prime Minister, he immediately called a general election and managed to increase the Tory majority from 17 to 60.
But his opinion poll approval ratings quickly fell from 70 percent to around 40 percent and he struggled to improve the areas he had little experience in, such as domestic and economic policy.
He also oversaw the disaster of the “Suez Crisis” when the UK faced humiliating defeat to Egypt over control of the Suez Canal.
Brexit news: Vote for Britain’s best Prime Minister since WWII in Express.co.uk’s poll (Image: EXPRESS)
Harold Macmillan (Conservative, 1957-1963)
Nicknamed Supermac, he helped speed up the decolonisation process, distanced the UK from apartheid and was a big player in the Nuclear Test Ban Treaty negotiations.
He was half-American and the son of a publisher, who was educated at Eton and Balliol College, Oxford and served in both World Wars.
