adhdad, I can think of following books. I haven't used any of them yet but I am planning to go to local WHSmith to have a quick look.
1) CGP level 6 (work book)https://www.cgpbooks.co.uk/Parent/books ... ook_ML6W21
2) CGP level 6 (Tests)https://www.cgpbooks.co.uk/Parent/books ... ook_ML6B21
3) CGP 11+ Maths practice papershttps://www.cgpbooks.co.uk/Parent/books ... Flip_MHTE1
4) FPTP (first past the post)
Numerical reasoning Book1 and Book2
5) Someone mentioned about the superselective maths book on amazon. I think it is this one -http://www.amazon.co.uk/11-Super-Select ... tive+maths
6) Question papers (past papers private schools) -
HABS boys/girls, North London consortium, Manchester grammar, Bancroft, Magdalen, St. Albans, Trinity, Whitgift, Reigate, City London boys/girls, St paul's, Godolphin and Latymer.
Hope this helps.