It's easy to forget that Alan Sugar is a Labour peer (and a significant party donor [2]) but he is and he's just become the first Labour politician to come out against Ken Livingstone. On Twitter, Sugar wrote: "Livingstone must NOT get in on 3rd May".

SKY doing live Mayoral interview with candidates at 8pm today Johnston v Livingstone is real issue. Livingstone must NOT get in on 3rd May

— Lord Sugar (@Lord_Sugar) April 19, 2012 [3]

After users pointed out that Livingstone was the official Labour candidate, Sugar posted an even more provocative tweet.

I don’t care if Ed Miliband is backing Livingstone . I seriously suggest NO ONE votes for Livingstone in the Mayoral elections

— Lord Sugar (@Lord_Sugar) April 19, 2012 [4]

Given Sugar's celebrity status Labour will be reluctant to discipline him but he has all but endorsed a rival candidate ("Johnston (sic) v Livingstone is real issue," he wrote). Yet given that Ken openly campaigned [5] for a non-Labour candidate in Tower Hamlets (independent Lutfur Rahman) he can hardly expect unquestioning loyalty from others.