He can make the target clear, but in my opinion it isn't feasible unless it's a simple cash transaction where he can skip most of the checks. Realistically if you would rather pull out than pay the £15k stamp duty I'd be seriously considering not proceeding at the moment. Obviously pulling out means whatever you decide to buy will incur stamp duty in the future. 8 weeks (with 2 bank holidays) would be pushing it for a simple sale at a very quiet time for solicitors, at the moment things are absolutely mental. I think if I was you I'd be feeling comfortable and safe that you'll complete before the following stamp duty jump in September and the June one would be a "we're just going to have to pay it" unless some miracle happens.