Boris Johnson is ambushed outside City Hall by campaigners YOUTUBE - KATYANASIM2009

THIS is the moment that Boris Johnson was ambushed outside City Hall by an angry group of campaigners for rape victims.

The amateur video of the London Mayor struggling to retain his composure while perched on his bicycle has become an unlikely YouTube hit.

Johnson has come under fire over a promise to improve facilities for victims of sex crime. Before being elected he had pledged to increase funding for rape crisis centres by £744,000 a year, or a total of £2.23 million over three years - almost double the £1.4m that has since been promised, according to a Labour spokesman.

The Mayor has taken steps to defuse the row, promising to open a new centre in Ealing, west London. At present rape victims in London only have one source of help, in Croydon, south London.

Johnson said £375,000 will be made available over three years to support the Ealing centre, while £260,000 will be spent boosting the Croydon helpline.

The money comes from £1.4m set aside earlier this year as part of his drive to combat violence against women.

But it is unlikely to silence his increasingly vocal critics, who want the mayor to meet the full amount he promised before coming into power.

It has emerged that the Croydon-based helpline has been so underfunded that only one in five calls have been answered.

Johnson admitted Londoners have suffered from "appalling under-funding" of rape crisis for far too long.

He said: "It is staggering that there was just one rape crisis centre for a city of seven million people. Today we are taking the first steps to redress that injustice.

"It's about time that the Government follows our lead and provides these hugely important services with the secure long-term funding they need rather than the piecemeal approach which has characterised their historic neglect of funding for rape crisis centres in the past."

The poor quality of services for victims of sexual violence has been a thorny issue for Johnson.

Last year the number of reported rapes in the capital soared by 15 per cent as domestic violence also increased.

Senior police officers believe that just one in 10 women who have been raped or sexually assaulted come forward.

They hope better facilities will help investigators improve the extremely low conviction rate for those accused of rape.

Johnson also plans to open two more rape crisis centres in east and north London, probably with the support of local authorities.

Kit Malthouse, deputy mayor for policing, said: "Today's announcement is an extremely significant first step in increasing help for women who have been raped or assaulted."

Jason Stacey, the leader of Ealing Council, said work has begun to identify possible locations for the centre.

Yvonne Traynor, head of Croydon's Rape and Sexual Abuse Centre, said: "This funding is a real boost for us.

"At the minute we can only answer about one in five calls made to our helpline. By doubling the number of staff manning the lines we will now be able to help twice as many callers.

"Women in London deserve better rape crisis services that are properly funded and this money is an important step in the right direction."

• The Rape and Sexual Abuse Support Centre helpline is 0808 802 9999. It is open between noon and 2.30pm and 7pm and 9.30pm every day.