UK Prime Minister Boris Johnson became prime minister in the summer of 2019. Since then he has overseen Brexit, won a general election and led the country through the pandemic. In opinion polls his Conservative Party remains ahead of the main opposition Labour Party. But he is facing a series of questions that opposition parties say he needs to answer. Here is a guide.

ISSUE ONE: WHO PAID FOR THE REFURBISHMENT OF DOWNING STREET FLAT?

When someone becomes prime minister in the UK they move into Downing Street - with their offices at 10 Downing Street, and the official flat next door in 11 Downing Street (thanks to them being inter-connected the prime minister does not have to pop outside to get from one to the other).

Because each prime minister has different tastes, there is a taxpayer-funded $42,000 allowance for maintaining and furnishing the official residence each year. And since moving in with his fiancee Carrie Symonds - they now have a baby son too - the couple decided to change the decor favored by his prime ministerial predecessor Theresa May.

It is not known how much the revamp cost but some UK newspaper reports suggests that the transformation of the flat may have cost as much as $280,000.

Ministers have said Johnson has paid for the work himself, but it is unclear whether the refurbishment was initially financed by a loan of some kind - and this matters because politicians are required to register or declare donations or loans.

The prime minister's former chief advisor, Dominic Cummings, who has fallen out with Johnson, said last week he told his then-boss last year that alleged plans to ask donors to pay for the renovation secretly were "unethical, foolish, possibly illegal."

Now, the Electoral Commission, which regulates political donations in the UK, said it had started an investigation, saying: "We are now satisfied that there are reasonable grounds to suspect that an offense or offenses may have occurred.

"We will therefore continue this work as a formal investigation to establish whether this is the case."

The issue was raised at Prime Minister's Questions by the leader of the opposition Keir Starmer, who asked who initially paid for the work.

In response, Johnson said: "The answer is I have covered the costs."

He added: "I have conformed in full with the code of conduct and the ministerial code and officials have been advising me throughout this whole thing."

ISSUE TWO: DID JOHNSON MAKE 'BODIES PILE HIGH' COMMENT?

The Daily Mail newspaper reported on Monday that, while opposing calls to bring in a lockdown in the UK last autumn, Johnson said he would rather see "bodies pile high in their thousands".

Johnson has denied saying it, although the allegation has since also been reported by broadcasters ITV and the BBC, citing unnamed sources.

At Prime Minister's Questions on Wednesday Johnson was asked about it by Labour leader Keir Starmer. Opposition parties say that if it turns out to be true that Johnson uttered the phrase, he would have to resign. Johnson categorically denied saying it.

He added that taking a decision to impose a lockdown was a very "bitter" and very "difficult" decision because of the knock-on impact it would have - but it was thanks to the lockdown and the "heroic efforts of the British people that we have got through to this stage," where more than 25 percent of British adults have now had a second dose of a COVID-19 vaccine.

ISSUE THREE: TEXT EXCHANGES WITH ENTREPRENEUR JAMES DYSON

Opposition parties have also called for an inquiry into lobbying after text message exchanges between Johnson and the billionaire businessman James Dyson were leaked.

These messages included Dyson seeking tax assurances from the PM to work on a project to manufacture ventilators in the early days of the coronavirus pandemic.

The BBC reported Dyson contacted Johnson directly, who replied: "I will fix it."

Dyson said it was untrue he tried to "extract favors from the prime minister" and said he was not close to Johnson and had not met him since 2016.

Johnson said last week he would make no apology for giving the assurances to Dyson secure ventilators to "save lives."

The leak of the text messages led the government to launch an inquiry into who leaked them.

ISSUE FOUR: WHO LEAKED PLANS FOR THE SECOND LOCKDOWN?

That is not the first leak inquiry.

Johnson's government was forced to bring forward the announcement of last November's COVID-19 lockdown after details of its plans were published in several newspapers.

The inquiry is said to be on-going and although some newspapers suggested the PM's ex-advisor was behind the leak, Dominic Cummings posted a detailed blog post on Friday denying that. He added that Johnson had been told by the country's top civil servant that Cummings was not behind the leak.

Cummings also alleged that Johnson had suggested stopping the leak inquiry if it implicated a friend of his fiancee.

Downing Street responded by saying: "The PM has never interfered in a government leak inquiry."