Who are the legal Sugababes?

As predicted, the lawyers have had to get busy to try to seal the Sugababes' line-up changes. Officially it's being stated that Jade Ewen hasn't yet signed her contract and as a result the new band has had to pull out of a gig.

Pop stars are notoriously reliant on their managers - and vulnerable to them - in protecting their rights. But sometimes managers miss a trick and sometimes stars do something clever. The past few decades have seen many legal battles in the courts over the rights to names of different bands.

So who does own the name? There's an added complication that Keisha Buchanan is listed as a co-writer on a great many songs - possibly including those on Sweet7. Asked about this on Twitter, Keisha has replied:
"maybe;-) lol but im all about staying positive. That would be so mean & bitter, im not like that:-) Good luck to em i say"

Keisha reputedly signed a deal in which she agreed to leave the band and in return was given a solo contract with Island Records and possibly an additional pay-off. So the odds are she has already signed away all her rights to the band's name. Did Mutya and Siobhan do the same?