I don't think you can use debit cards without swiping them like you can credit cards.. can you?
Besides.. I don't think I'd want to use something that has access to my bank account on the internet, whereas credit cards you can cancel easier, and also dispute charges.. try disputing a debit card charge with the bank.
Yes, you can, most shop sites, Amazon / Play / Ebay etc all take them in the UK. If you have a PayPal account and you've registered your debit card with it, contact Russ and you can subscribe that way.