The best way to find high quality locks is to visit high quality bike stores. Locks that are sold in the USA under one brand name are often sold in the UK under a different brand name. So, the OnGuard Pitbull may be sold under a different name in the UK. The staff at a good bike store (not a chain store, discount store, or general sporting goods store) can show you which of their flat key D-locks are best for your needs.
As a "rule of thumb", use the shortest D-lock that works for your bike. You don't want to leave open space that allows access for prying and leverage tools. Few people need a five inch by ten inch lock.
"Sold Secure" tests bike locks sold in the UK for insurance companies. They have given "gold" ratings to the best models from Abus, as well as the "Oxford Magnum", "Squire Paramount Plus", and "Squire Urban Paramount".
Squire appears to be the major UK supplier for top quality bike locks. Their web site is at www.squirelocks.co.uk
A "Sold Secure" rated lock has been tested to stop a trained professional, using a full kit of tools, for at least FIVE minutes. That means, if you will be leaving your bike on a public street for an hour or so during the day, or for more than fifteen minutes in the middle of the night, you really need to be combining two or three different "Sold Secure" Gold rated locks. Leaving two of them at your place of work, and carrying one of them on the bike will reduce the "load" while commuting to your job.
Last edited by alanbikehouston; 10-12-04 at 04:21 PM.