Labour leader Ed Miliband has described Boris Johnson as a "good showman but not a very good mayor".
Speaking to ITV London, Mr Miliband said that while the London Mayor was a "fun guy" it was not enough to be a good Mayor.
However, the Labour leader insisted comedian Eddie Izzard - who has announced his intention to stand as London Mayor - was welcome to stand for Labour in the 2020 contest.
More top news
London Underground and Southern rail workers could walk out at same time in combined pre-Christmas strike.
Greyhound cross 'Bud' was Battersea Dogs & Cats Home's longest staying resident after being overlooked hundreds of times.
Police investigated a parked vehicle on Bread Street, EC4, after it was reported to police around 10:30am this morning.