Went to my local Gamestation (28 Broadmead, Bristol) to buy Overkill and found that it was on offer for £17.49 vs £19.99 online. And yes its brand new not pre-owned.
I asked the guy behind the counter and he confirmed this to be nationwide. Have seen quite a few for £14.99 on hotukdeals but have not been able to get my hands on any of those instore deal..
I thought i will share this with the community. Hope it helps.