Before .uk if you agreed to buy a .co.uk on Sedo, you would have paid and got the .co.uk. The agreement would have been fulfilled, end of story. As I see it, today if you agree to buy a .co.uk on Sedo and you get the .co.uk, the agreement has likewise been fulfilled. Legally, no doubt the .co.uk domain minus the .uk rights can still be referred to as the .co.uk domain, just as it was before the .uk launch. If Sedo's agreement has not been updated I don't think there's a legal issue here. Having said that I think registering the .uk after agreeing the sale is a lousy trick to pull, but since you haven't paid yet, you can still get in touch with Sedo and demand that the .uk is also transferred. If enough people do this and sales agents are inconvenienced they may wake up and update their system.