This is an electronic debit system for UK players who would like to play online casino games without having to use a credit card. For one, there is no interest tag ons, neither is there any chance of being denied, as is the case with many credit cards transactions.
Since 2002 though, Switch cards have been slowly merging with Maestro cards, which is the international debit card system of MasterCard. Switch is also the sister card of Solo Card.
The merger was to assist brand recognition of Maestro cards, but since UK residents are so familiar with the Switch card, transactions are still being accepted here.
The most popular provider of the Switch/Maestro cards is HSBC which includes a number in the card that indicates how many times a card was issued to a particular account. This forms part of their security system which helps to avoid problems when the card gets lost or expires.
Being a debit card, all you need to do is to transfer funds to your Switch card which you can then use to gamble online. Check with online casinos if they accept Switch cards, or Maestro cards. If yes, clicking on the cashier tab will start the deposit process and almost immediately, you can start playing.