If it was a big job, then I'd consider paying some in advance for materials etc, but on a job of £2000, then any builder, even a one man operation, should have enough financial stability to stand the initial outlay on materials of that value. If he hasn't, I personally would be very wary of even using him to do the job, and no way would I lay out any cash upfront.
If the guy doesn't even have 2k in his own funds, what will happen if you have any problems? He's highly unlikely to be able to afford to come back & rectify for 'free', as he'll need to be on the next paying job.
If I were you, I'd wait for someone you have been recommended to use, even if it takes it to after Christmas. If you don't have any recommendations, then use someone you just get a good feeling for, and ask them for any examples of work in your area they have done that you can check out. And don't part with anything over £200 up front.