Hi James

The short answer is yes, with the caveat of don't expect to have a nice lawn afterwards! Laying on top of the old turf is not a substitute for properly preparing the ground. Check out the bbc page http://www.bbc.co.uk/gardening/basics/techniques/lawns_layingturf1.shtml (other advice is available)

Hi, welcome to GoY, I agree with Urbanite, if you lay turf on top of your old lawn, then any problems you had with the old 1 will resurface in the new 1, Derek.

Better to start again and work the ground as you can get it nice and level and then turf it or sow seed maybe later on in the spring.