Assuming that the instument is complete and not "damaged" - ie. warped bowed or twisted neck, all frets there and fairly "true" I would have regarded £60 for a vintage Windsor a fair or good price 20 years back.
Sounds like a bargain unless it suffers from the above defects. In that case it might be worth repair - if you can find a competent craftesman repairer. You might also wnat to pay that for a wall decoration.
Acording to their websites Hobgoblin have ones for sale at £350 and for £450, so the price is excellent if the instrument is playable.

Some useful links :-
http://www.andybanjo.com/faq_2.htm
British Banjo Makers Part 4
Somebody's links page
Quack!
Geoff.