Hmm, nice frame but a vanilla name. I'm sure it will ride really well, but the world is full of old rim-braked racing bikes.
I wouldn't pay more than £200. Clearly it's not been cleaned up or maintained in a while, and it's been stored somewhere damp. It will need all the bearings opened up and re-greased as doubtless the grease is dried up.
It's got some nice bits but there are plenty more out there like it and it's a buyer's market.