Brit Index: Directory of uk websites listed by category. Large directory with lots of sites in lots of categories.
Excite uk: More of a portal than a search destination these days. Large directory but top places full of sponsored listings...
Great British Pages: Large directory of UK websites. Easy and straightforward to use - some of the results are sponsored listings provided by Overture. Also, beware of pop-unders.
Hoover's online: Hoover's online UK business directory. Search by company name, location, even by Dun & Bradstreet no. Over 1.7 million UK business listings.
Lifestyle UK: Lifestyle is a huge directory of UK websites. The top spots in all listings appear to be paid listings with the reviewed directory listings lower down.
NetLondon: Net London covers all things London. The long established directory contains some excellent reviews of London themed/based websites.
Scoot: UK directory, find local businesses, cinemas, leisure facilities etc. Scoot is huge online relephone directory and more.
Search Uno: Search Uno bills itself as the 100% pure web directory. The first hal dozen links are affiliate links. Scroll down the page for the reviewed listings.
Sgt Search: Sgt search bills itself as the free uk web directory. All listings in the directory are hand-reviewed and are added free-of-charge. Large selection of uk websites.
UK 250: UK web directory that has 250 categories with no more than 100 websites per category so as not to serve too many results. This is a paid business listigs directory.