Joining the Dots by Alan Bullard, books 1-5, published by the Associated Board, are a good approach with a  general musicianship slant.

Improve your Sightreading and Perfect your Sightreading, a book per grade, by Paul Harris, published by Faber are also excellent.

Sightreading is often a vexed and feared subject. Does anyone have any ideas or experiences they would like to share? I think the blog would be a good starting point for sharing thoughts on this subject. Do please take part!