This was recently available at Asda for £4.93 but that has since expired. The film is now part of DVD.co.uk's 2 HD DVDs for £10 or is £6.95 on it's own.
To avoid any confusion or accusations of fib telling - the stand alone price is listed adjacent.
This may be of use if there is something else in to get in the 2 for £10 deal - the Optimum discs seem to be quite pricey elsewhere. Quidco too!