I did a search for these and results came up with either out of stocks or discontinued, others were so old, the deal probably doesn't exist (instore deals), so I though I'd post this as the company that sells them on amazon (LPC Shades with 99% positive feedback) has stock.
• Write-once Double Layer DVD+R
• 8.5GB Native Capacity
• 8x Write Speed
They're priced at 86p with £2.99 p&p, so you pay £3.85 in total. I think it's a good price for a pack of 10 dual layer discs that have good reviews.