This hilarious film is £2.99 at Play, and you can get £1 off using the voucher you get if you recommend Play to a friend (you sign up your own second email as the "friend," create the account and use the £1 voucher yourself on the new account!).
I found the info about a £1 voucher on MSE, though it said it came from HUKD. I couldn't find the original voucher post, though. Here's the link to recommend a friend and get the £1 voucher: http://www.play.com/campaign.aspx?campaign=7312&cid=7405285.