http://www.yale.co.uk/en/yale/couk/ProductsDB/?groupId=934&productId=50307" onclick="window.open(this.href);return false;
This is the lock I use. Cost about £15 from tesco. Seems like it's very good quality. I'd imagine the weakest link in the whole lock would be the steel supplied by uber (not a criticism at all, very happy with it), so anything more would be overkill in my opinion. As we always say, if they want it enough they'll have it.