Suppliers

Components

Futurlec - Good supplier, very cheap SMD to DIP converter's which are useful for prototyping.

RS Components - Not always the cheapest, but you can collect from a trade counter. Shipping is also quite expensive if not a large order.

Farnell - Larger selection than RS and free shipping, however there is a minimum order to qualify.

Digikey - Even larger selection than Farnell and free shipping on orders over £50. However, if you don't meet the £50 threshold the cheapest shipping option is £12.

eBay - Always a good place to start, direct access to Chinese sellers without the risk.

Tools

Circuit Specialists - Soldering equipment, blackjack range is very good for the price.

Wholesale Chinese Suppliers

IC2IC - Good for large orders, also able to find discontinued components.