Well first of all, I think you have a bargain -assuming it's in decent condition (good tyres, no dents, drivechain not worn, etc), which is hard to tell from the photos. Dawes are touring classics.
What would I do? Check the bottom bracket, wheel bearings and headset for smoothness and visually inspect the frame carefully for anything that might be questionable and then thoroughly clean it and lube it with proper lube. Then I'd probably spend some money and buy some brake levers with hoods -these will allow you another hand position. Secondly, it looks like those handlebars have been wrapped with electrical tape -get some decent cork tape. Thirdly I'd probably get new brake and gear cables all round. Finally, I'd invest in some Koolstop brake pads to improve braking performance. I'll guess that all this would cost maybe around 60 pounds depending on the brake levers you buy?
Once that's all done, I'd just ride it and enjoy. In the future, and depending on how much you like the frame, I *might* invest in a newer drivechain with barcons or STIs, but that is more personal preference. Drawbacks for this bike? If you really want that newer drivechain and since the wheels are 27", a newer drivechain would mean a new hub (cassette system rather than freewheel) and either you'll have to relace the wheel yourself or pay someone to do it. Those 27" wheels are a drawback as well in terms of less tyre and rim choice, but not enough to prevent it being a good bike, more of an inconvenience.
As I said, assuming it's in good condition, I'd have bought it! However, if you want STI or barcon shifting and 8+ speeds, then maybe I would have given it a second thought and asked for a lower price (the price of purchasing a new drivechain as described is really so close to the cost of a new bike with that drivechain that I'd recommend just buying that new bike). But... the frame, it's lovely and a classic.
One last caveat: I do notice it's a double -depending on your load and fitness and gearing, this may make this bike hard on you on steep hills.