Visa application details are on the website of the Russian Embassy: http://www.rusemblon.org/logon_en.htm
(Click 'Tourist Visas' in the panel on the left).
You'll see, from that page, that you must submit "Tourist Confirmation (in Russian language) of acceptance from the authorized Russian travel agency or a hotel, registered with the Russian Ministry of Foreign Affairs. The confirmation must contain the agency�s reference number and registration number. You can obtain this from the hotel or a British travel agency". In practice, that means that you can't directly apply for a visa yourself. You have to use the services of a recognised travel agency. If you book through such an agency, they'll do the work for you. Otherwise, Intourist can make the arrangements. They'll charge you �90 for a single entry visa, with 6 to 10 days processing time. (There are higher fees for multiple entry visas or for the one day service): http://www.intouristuk.com/run.php?fcnt=visa&s ession=EMB010243206885&agent=&name=