I think you'll find there are a lot of people in the same boat, i've got two properties i would love to be shot of so as to be able to go on to my next project, the town house i got for 240 in 2006 has had two offers of 250, so until i get my 270 i shall just have to carry on letting it out, if there are people out there waiting for the market to fall even further you may have a long wait, alternativly when a property becomes free you can rent off me.
I'd take the £250k.
Rents are due to collapse as they were always based upon what housing benefit would pay out. Interestingly the price of houses in the sub £250k market was also based upon what the taxpayer would pay via housing benefit.
Now housing benefit is being cut, rents in the private sector will have to drop, and that means the price of houses in that market will also drop.
So take the £250k as you won't get that once the cuts kick in.