London  - Tickets for Michael Jackson's This Is It comeback tour in Britain this summer went on sale in London Friday as organizers raised the number of performances to 50 due to "overwhelming demand."

The US superstar announced in London last week that he would give an initial 10 concerts from July in what he called his "curtain call" in the British capital.

However, following strong pre-sale demand, organizers have added another 40 dates, prolonging the Jackson series into February 2010.

Jackson, who has returned to the United States for rehearsals, is said to be "ecstatic" about the response.

The concerts will be staged in London's O2 Arena, the former Millennium Dome, in the revamped docklands in east London.

Fans from around the world are expected to flock to the venue, which can hold 20,000 people.