In Costco they currently have 2 x 60 Surf laundry capsules Tropical Lily and Ylang Ylang for £4.90 plus VAT, so £5.98 in total. This works out at 5p per wash. In Sheffield, but I presume this would be national. The big box of powder Surf is still £11.98 after VAT for 120 washes, so only the capsules on offer.
Costco 2 x 60 wash Surf laundry capsules £5.98 (5p per wash). Tropical lily