Most major high street banks and currency exchange providers in the UK can pre-order Roubles (Russian currency). If you plan to buy roubles in Russia, you should take US dollars or Euros to exchange. Only change money at banks, hotels and airport exchange bureaux. It is an offence to change money from street traders.
Most hotels, restaurants and larger shops accept credit cards. There are ATMs in most major cities. Consider informing your bank before you travel to Russia to avoid having a temporary stop on your card. Travellers’ cheques are not widely accepted.
It is illegal to pay directly for general transactions with dollars or Euros.