Amazon has launched a new trade-in deal for prospective Xbox One owners, which lets you get an extra £30 discount on selected Xbox One bundles when you trade in a PS3 or Xbox 360 towards it. The PS4 is also included in the promotion... though we suspect that takers may be pretty slim on that front.
As explained on-site, you'll get the trade-in value of your old console plus an extra £30, so long as your old kit is in decent nick. For example, if you've got a 'like new' Slim 250GB, you can get somewhere around £91 credit all-told (if you're lucky), bringing down the value of one of the Evolve Bundle to around the £200 mark.
Naturally there's a lot of 'ifs' involved, and we'd recommend reading the T&Cs thoroughly. Thanks and credit to fandangoxx @ HUKD for the spot!