Chris Evans has quit Top Gear, announcing that "my standing aside is the single best thing I can now do to help the cause".The presenter is understood to have become tired of the constant press sniping about the motoring show, which recorded poor viewing figures.The announcement comes after police confirmed yesterday morning that they are investigating allegations of sexual assault after the presenter was accused of grabbing the breasts of a female colleague in the 1990s.The Met confirmed that a woman had made an allegation of "non-recent sexual assault" to officers on May 23, six days before Evans' newly revamped Top Gear returned to the BBC. Police said the allegation related to "incidents in the 1990s". It's Evans or me - Le Blanc warns Top GearMatt LeBlanc is allegedly planning to quit Top Gear if his co-host Chris Evans is not removed from the team first, sources have claimed.Heat Street, a news website, reported in May that a former colleague of Evans had complained that he had exposed himself to her and grabbed her breasts.Evans has previously denied the claims, saying they amounted to a "witch-hunt".Neither the BBC nor Evans' representatives would comment on the claims yesterday. A spokesman for the corporation said the presenter would continue to host his Radio 2 show.A friend of Evans said: "Every single day he's been accused of something else."In the end you just think 'f*** off'. If the show had done better in the ratings, perhaps the battering would have been less fierce. Who knows?"Under Evans, Top Gear has performed poorly in the ratings, and sank to a new low of 1.9million viewers on Sunday. ..