Ill reccomend a cheap and easy to access system (since you live in the UK) aka Adire, RE, Image Dynamics ect = hard to get over there.
http://ikesound.com/product-product_id/3352
Single Type R Sub.
http://ikesound.com/product-product_id/3352
Type R Components
+ another set for the rear for which ever size fits. (does not have to be a component either)
http://ikesound.com/product-product_id/1283
Decent amp.
and depending on how much you would like to spend on the HU
http://ikesound.com/product-product_id/2826
or
http://ikesound.com/product-product_id/2827
or
http://ikesound.com/product-product_id/2089
or
http://ikesound.com/product-product_id/2824
or
http://ikesound.com/product-product_id/2825
& find yourself a 4 gauge wire kit to hook up for power.
(i am a huge fan of alpine all around the board for an easy to setup system.)
& if you want find a decent 4x50 4x75 or 4x100 amp to power the speakers. (it enchances the experience completely.
-ALSO have a professional build you a proper box to spec. Prefabs blow chunks.
-NOW juju is probably going to have a much different recommendation, (MORE euro brands and or pioneer infinity stuff...) but THIS IS MY my solution to a problem. Alpine has never let me down.