A leaked email has revealed that the London Assembly Labour group blocked questions that could be “deeply embarrassing” to Sadiq Khan in the run up to the mayoral election.

The email, which has been seen by the Local Democracy Reporting Service, revealed that City Hall Labour group officers rejected four proposed questions about the controversial Silvertown Tunnel ahead of a Mayor’s Question Time (MQT) session earlier this year.

The questions focused on whether Sadiq Khan had paused to rethink the modelling of the project in light of the Covid-19 pandemic, but they were rejected on the basis that “they could be deeply embarrassing to the mayor, especially so close to the mayoral election”.

The £2 billion Silvertown Tunnel is a proposed road tunnel that will connect the Greenwich peninsula to west Silvertown, but has been criticised by politicians, activists and climate experts over the potential impact it will have on local air quality.

One of the questions that was rejected by Labour group officers asked the mayor why PM2.5 pollution, a type of particle pollution caused by vehicle tyres and road wear, was not taken into account in the air pollution assessment for the project.

A spokesperson for the Labour group said that “from time to time we have too many questions for MQT, and we have to prioritise on the basis of what matters most to Londoners”.

The spokesperson said: “This meant that in recent months, we’ve prioritised questions on tackling crime, the capital’s economic recovery, job creation, and cleaning up our toxic air.

“Labour AMs are committed to delivering full and proper scrutiny – including on the Silvertown Tunnel, on which we’ve submitted written questions for the last two MQT sessions.

“Scrutiny takes place at different levels across the GLA and indeed the GLA Oversight Committee, which was chaired by a Labour Assembly Member, was looking into a number of issues on Silvertown during this same period and did that through correspondence with TfL.”

Following Sadiq Khan’s re-election, the Labour members within the London Assembly were accused of having “abdicated their responsibility to hold the mayor to account” by City Hall Conservative leader Susan Hall after a disagreement about the allocation of scrutiny committee chairs.

None of the Assembly’s scrutiny committees will be chaired by Labour members this mayoral term after the group rejected an agreement proposed by the other three parties in the Assembly.

At the time, Labour group leader Len Duvall accused the other parties of forming a “coalition” and said that “we don’t have to chair any committee to play a full part in scrutiny”.