Use the code allfel15 at checkout, offer ends 31st March.
Refills are £13.39 with the discount (were £15.75).
Diffusers with vial included are £18.85 with the discount (were £22.18).
They are also doing 10% off Frontline when you buy more than one pack but the price for 2 packs or more (£17.45 per six pack) is the same price as a six pack was a few months ago so no great bargain. One pack is currently £19.39.