Or if you don't mind waiting for a bit to save a few pennies (literally) then it's £27.99 at Play 3000, but currently none in stock (http://www.play3k.com/products/product.html?/productid=P453F64077738C)
Also BlahDVD is a good option if you're a 'new customer' to them as you're eligible for £5 off a £30 first order (http://www.hotukdeals.com/deal/20422/5-off-30-spend-for-new-accounts-bla ). Wii Play is £32.99 with them, with £5 off that's £27.99 and also 5% quidco, makes it £26.59 possibly...
EDIT (again) now in stock at eBuyer and works out at £27.56 until the Google checkout offer ends
EDIT (AGAIN) Cheapest price now by a few quid is at movies and games online...works out at £22.99 with Google checkout...grab it while you can...finally jumped ship and ordered one meself (even though my Wii hasn't turned up yet)