I can't, but if I could, I wouldn't! At least, not unless there was a candidate other than those from the three main parties - Green, perhaps? Or Monster Raving Loony - some of their policies have now been implemented.
I no longer have any loyalty to the Labour party - Blair changed it out of all recognition and now I cannot see any difference between it and the Conservative party.
I might vote for an individual who had shown real commitment to the job and his/her constituents, regardless of their party allegiance.