Ellis brigham has a store located just off Covent Garden, which offers an extensive range of ski's and outerwear, however tends to be extremely expensive.
Snow and Rock has a store located also just of Covent garden, which has 3 floors offering ski outerwear, helmet products and goggles, and a dedicated basement just for hardware, however like ellis Brigham it can be expensive and cheaper to shop else wear.
near covent garden there are also a Patagonia store, and 4 Cotswold outdoor centres, which offers a large range of outerwear and clothing, but limited ski's and hardware.
Ride king, is also located on the other bank of the thames river, and also Finches ski's and sports, however i have not been to these stores, but i know they are not chain stores, like snow and rock.
i hope this helps, online there are also stores such as 2seasons, freeze pro shop, Surfdome and extreme pie which all offer an extensive range of hardware and software at competitive prices
Hope this helps !!..