Maths the Basic Skills (June Haighton) is an excellent book from Nelson Thornes (ISBN 0-7487-7700-8). Covers all numeracy elements from E3 to L2 with clear explanations and lots of practice exercises (answers at back). Great for students studying for Level 1 or Level 2 numeracy as they often need to dip back to Entry 3 in some areas.
Since publication in 2004 the book has been fully updated (now up to the fifth edition)
Related packs of worksheets and workbooks for Entry 1 and 2 numeracy (one pack each for number, measure and data) are available from Nelson Thornes
You can also view sample pages and free worksheet answer sheets at http://www.nelsonthornes.com/mathsthebasicskills/student_books.htm