British Prime Minister Boris Johnson said Saturday he would not undergo any "psychological transformation" despite this week's election drubbing and a slew of bad headlines, which included claims he wanted a lavish tree house built for his son. 

The beleaguered premier recently survived a confidence vote in his leadership, but was left severely weakened after more than 40 percent of his MPs called on him to quit.

His position became even more perilous on Friday after he lost two key by-elections in highly symbolic seats.

Johnson told BBC Radio's Today programme that if critics "want me to undergo some sort of psychological transformation, I think that our listeners would know that is not going to happen.

"What you can do, and what the government should do, and what I want to do, is to get on with changing and reforming and improving our systems and our economy."

Daisy Cooper, deputy leader of the Liberal Democrats who delivered one of the crushing by-election defeats, said the comments showed that "this leopard has no intention of changing his spots".

Johnson's popularity plunged during the so-called Partygate affair, in which he and scores of his staff were fined by police for lockdown-breaking gatherings in his Downing Street office.

Spiralling inflation and widespread strikes are also piling the pressure on the 58-year-old, who told the BBC he must "humbly and sincerely" accept the criticism.

Adding further fuel to the fire, the Times on Saturday reported that Johnson drew up plans for a costly tree house, complete with bulletproof glass, for his son Wilf in the grounds of Chequers, the country house of UK prime ministers.

The paper reported he approached a Tory donor about funding the project, but eventually ditched it after protection officers warned it was a security risk and aides told him the cost would be hard to defend.