Its advertised in the Metro that Best Buy are selling it for £29.99 on X360 & PS3 on the launch day. I think thats the best deal ive seen so far. Only problem is, there is not too many Best Buys around the country.
As above, any supermarket deals wont go live probably until the game is released, I wouldnt expect to see a price war with different stores dropping the price to £25 alone without it being part of some combi deal like buy points or a certain value of shopping
to get a discount on the game