He has made no secret of the fact he wants to take over every rail service in London -- and today the government appeared to back Boris Johnson's plans.
The Transport Secretary Patrick McCloughlin told London Tonight he had 'no objection in principal', to the Mayor of London having power over rail franchises.
He pledged his support as Mr Johnson officially opened a new route on the London overground service.
Our Political Correspondent Simon Harris has the story.
128 years after the circle line was completed, the capital now has a new orbital railway.
The final section of the London Overground - between Clapham Junction and Surrey Quays - has been completed and the line now runs in a full circle around the capital.
Today, the Mayor Boris Johnson climbed aboard for the official launch, joined by our Political Correspondent Simon Harris.
Transport Secretary tells ITV London he has "no objections" to giving Boris Johnson control of rail franchises. @londontonight
Patrick McLoughlin seems to be hinting at a significant u-turn in DfT policy. @londontonight
TfL sources think an announcement could come in the New Year. @londontonight
The Mayor will be trying out the new east London Overground extension this morning.
The new line from Clapham Junction to Surrey Quays, marks the completion of a £1.5 billion project to create an orbital service circling the whole of the capital.