The electrical current in London is 220-240 volts (coming into line with the rest of Europe at 230 volts), 50 cycles alternating current (AC); wall outlets take three-pin plugs, and shaver sockets take two round, oversize prongs. For converters, adapters, and advise, stop in one of the many STA Travel shops around London or at Nomad Travel.
Consider making a small investment in a universal adapter, which has several types of plugs in one lightweight, compact unit. Most laptops and mobile phone chargers are dual voltage (i.e., they operate equally well on 110 and 220 volts), and thus require only an adapter. These days the same is true of small appliances such as hair dryers. Always check labels and manufacturer instructions to be sure. Don't use 110-volt outlets marked "For Shavers Only" for high-wattage appliances such as hair dryers.
Nomad Travel (43 Bernard St., Bloomsbury, London, WC1N 1LJ. 020/7833-4114. . 52 Grosvenor Gardens, Victoria, SW1W 0AG. 020/7823-5823. .)
STA Travel (0333/321-0099. .)
Steve Kropla's Help for World Travelers. Information is available here on electrical and telephone plugs around the world. .
Walkabout Travel Gear. Offers some helpful advise on electricity; search for "Adapters." .