Well, if you look and see no vehicle approaching and then proceed, you are legal, it's not your fault if someone is exceeding the speed limit and is upon you suddenly.
But then try to prove it if it causes a smackdown. Bummer.

2005 Model . Two Fast Eddy stickers , a bell and a clock . She's Lola . She tinkles and keeps time . http://s649.photobucket.com/albums/uu211/britbike05/