Also spotted:
The Lyonesse Trilogy by Jack Vance for £3.99
https://www.amazon.co.uk/Complete-Ly...ncz+collection
10 titles in the Xeelee Sequence by Stephen Baxter for £3.99:
https://www.amazon.co.uk/Xeelee-Sequ...ncz+collection
Time's Tapestry by Stephen Baxter at £3.99:
https://www.amazon.co.uk/Times-Tapes...lection+baxter
(Note that the Destiny's Children series are a separate entry as well as included here.)
10 titles in the Psy-changling series by Nalini Singh for £3.99
https://www.amazon.co.uk/Psy-Changel...ncz+collection
The Confluence Trilogy by Paul McAuley for £3.99
https://www.amazon.co.uk/Confluence-...ncz+collection
The best way to look is to search Amazon for 'Gollancz collection' - about half the results are stand-alones, but the rest appear to be some quite good bargains.