"I think it's inevitable that he will have to resign from the assembly," London Mayor Sadiq Khan told ITV News London.
Former Conservative mayoral candidate Shaun Bailey came under pressure today to resign from the London Assembly after he was pictured at a Christmas party during last year's lockdown curbs.
Mayor Sadiq Khan said it was inevitable and 'a matter of time' before Bailey would have to quit his City Hall post. Political opponents demanded a fresh police investigation.
Bailey stood down as chair of the assembly's Police and Crime committee last night and failed to appear at today's scheduled meeting.
Labour, Liberal Democrats and Green Party assembly members signed a joint letter to Metropolitan Police Commissioner Dame Cressida Dick saying the photograph appeared to a show a breach of the law.
Bailey was pictured with 23 supporters at gathering in December last year. Some wore party hats, others held glasses of wine and a buffet was laid out on a table.
"I think it's inevitable he's going to have to resign from the London Assembly," Sadiq Khan said.
"I can't see how he stays on.
"I don't see how Londoners can have any confidence in him.
"I'm sure it's just a matter of time before he steps down, it's the right thing to do," Mr Khan added.
Grant Shapps said the rule breaking party at Conservative Party headquarters was "disgraceful".
The Transport Secretary said the event, which took place when London was under Tier 2 restrictions, would be "properly investigated" and several people had already been disciplined.
"It's disgraceful and that party was not authorised by the Conservative Party that was the mayoral candidate," Grant Shapps told ITV News.
"There were four individuals who were on secondment to that campaign in that picture.
"They have already been disciplined, we take it extremely seriously.
"I was following the rules, so was the rest of the country and I think the picture is disgraceful and it will be properly investigated I'm sure by whoever the correct authorities are," Mr Shapps added.