Boris Johnson's vanity projects as London Mayor have cost the taxpayer £1billion after he repeatedly ignored expert advice, critics claimed today.

The would-be PM has been accused of failing to 'read the paperwork' and being 'lousy on detail' during his term in City Hall.

Political opponents highlighted a series of major schemes that they insisted ended badly - including the aborted Garden Bridge, the Orbit tower in the Olympic Park, and Routemaster buses.

Steve Norris, a former Tory mayoral candidate who served as a board member on Transport for London, told the Guardian: 'These projects tell us that Boris never reads the papers and isn't great on detail.

Boris Johnson (pictured in Westminster yesterday) has been accused of failing to 'read the paperwork' and being 'lousy on detail' during his term in City Hal

'He could be incredibly profligate for the country. He's great on rhetoric but lousy on delivery.'

Mr Johnson has always defended his projects as major contributions to the capital, and blamed the former Labour administration for many of the cost increases. A spokesman refused to comment.

Mr Norris said the approval of new Routemaster buses, which met Johnson's manifesto pledge to bring back conductors on buses, was an 'egregious error'.

He said: 'I know Peter Hendy (commissioner of Transport for London) said we couldn't afford to run the buses with a separate conductor, but Boris decided to build them anyway.'

Mr Hendy refused to comment when approached by the Guardian.

Most of the conductors were later removed from the Routemasters amid claims they were costing £62,000 per bus per year to operate.

The total cost of the buses has been put at £321.6m.

An official report earlier this year found £53million had been spent on the failed Garden Bridge project - £43million of which came from public coffers.

The 'Boris bikes' cycle hire scheme has been highly popular among Londoners. But critics said it has left a bill for £225million so far despite being meant to cost the public nothing.

Soaring costs at the London Stadium, and expenditure on looking into the so-called 'Boris airport' project in the Thames Estuary were also highlighted by opponents.

Two second-hand water cannon purchased for police during Mr Johnson's tenure but never licensed or deployed were sold off by current mayor Sadiq Khan earlier this year at a £300,000 loss.

Political opponents highlighted a series of major schemes that they insisted ended in failure - including the aborted Garden Bridge (artist's impression pictured)

The race to be Tory leader and next Prime Minister is entering its last stretch as Mr Johnson and Jeremy Hunt prepare to take part in the final hustings of the campaign.

As both candidates prepared to stake their case publicly again, Cabinet member Amber Rudd insisted either man would have to compromise on EU withdrawal if they get the keys to Number 10.

And Prime Minister Theresa May is set to use a speech later to stake out her legacy as premier and give her overview on the state of national politics.

Change UK MP Anna Soubry, who quit the Tories over Brexit, was scathing about Mr Johnson last night, telling ITV News: 'He couldn't even be trusted to clean the loos.'

Meanwhile, the new president of the European Commission Ursula von der Leyen has insisted that Brexit could be delayed beyond the end of October if there was a good reason for postponement.