One of Labour's potential candidates to become Mayor of London next year has said the party must use the contest as a springboard to win the General Election in 2020.

Dame Tessa Jowell said the May 2016 battle to replace Boris Johnson as Mayor was a "very big moment" following Labour's disastrous performance in the General Election last month.

Speaking on the The Andrew Marr Show, Dame Tessa, a former cabinet minister, suggested Labour would have a "really serious" problem if it failed to win in the capital as it would go into the 2020 national poll without having won a "big" election in 15 years.

She said "We have got to get that winning determination back. We start in London, we start with the possibility of winning the London mayoral election next May.

"If we don't win next May then Labour will not have won a big election by the time we get to 2020 for 15 years. That is really serious.

"It's a very big moment and that's why Labour has to choose a candidate who can win, who can unite London and build one London. I think I'm that candidate."

She added: "The important thing is that Labour chooses a candidate who can win this election because the scale of our defeat five or six weeks ago shows that we kind of lost the art of winning the election. We have got to get that back again."

Dame Tessa's rivals to become Labour's Mayoral candidate include MPs Sadiq Khan, David Lammy, Diane Abbott and Gareth Thomas, and journalist Christian Wolmar.

Environmentalist Zac Goldsmith is widely seen as the Tory frontrunner while political veteran George Galloway will formally launch his bid to become mayor tonight.

The Respect Party leader, who lost his seat as Bradford West MP to Labour last month, has pledged to "build a city that benefits everyone, not just those dripping in gold".