The BS510 is Trelock's top of the range U-lock and although outwardly very similar to the 400, the extra 500g in weight tells you that it's not fashioned from the same stuff.
Whereas under handtool attack we could make the 400 bend into some very surreal shapes until it eventually popped, my 14 stone weight couldn't make this budge at all; this is one very tough lock. After the full five minutes we'd made some cosmetic damage and put a slight kink in the shackle, but the lock still operated perfectly and we'd be happy to keep using it. In test two, our power tool took apart the shackle in a little over 30 seconds and once it was cut we were able to rotate the shackle enough to remove the bike. This is one very tough lock, with an excellent strap fitting mount bracket too.