I agree that it is a really lovely guitar. I would ask for more photos and as has already been mentioned, as serial number to check.
The seller lists it as "new". I guess I would want to know the circumstances of how they have a new guitar for sale, unless they are a dealer. If the guitar is previously owned but unused it should be listed as "used" but in the description it could be described as "mint" condition. This affects price. If it is new then it is listed at the low end (for the UK) and is an extremely good deal. If it is used (even if it is mint) it is at the high end of the price range and I would not expect to pay much more than that.
Also, a lot of us ES-120 owners like to mod our guitars with new pickups, etc. Just because the original pickups are currently installed in the guitar doesn't mean the owner hasn't swapped them out for replacements and then put the originals back in. Again, this is no problem if they knew what they were doing. I bought my ES-120 pretty recently (and it the same part of the UK!) and that is exactly what had been done. The problem was the previous owner was a maniac with a soldering iron! What a mess. Fortunately for me I have a good friend (an electrical engineer) who helped me fix it all. We ended up replacing the wiring, pickups, pots, switch, and caps to a higher spec.
One more thing, the seller doesn't like paypal. Paypal does cost you but you buy a degree of peace of mind. If you send money in some other way, take precautions, friend...maybe someone else can advise you on this. I always use paypal.
It you like the guitar go for it...it's well worth ?640...but my advice is get more info. Good luck.