I believe these are the Direct Replacement speakers everyone goes on about on here but I've never heard them.
http://caraudiosecurity.com/shop/product/products_id/10868.html
£40 isn't going to get you a great set of Speakers though TBH.
What brand would you recommend mate? I am lookin to do my speakers soon, not very clued in, dont wanna spend mega money just something middle of the road price wise. Prob just gonna replace the four door card speakers.