Add 2 of the White Cap Button Mushroom kits to checkout.
In the 'Catalogue/Newspaper' code box, add code WSE355
Proceed, and you will only pay £2.77 instead of the £12.77 it should cost.
Don't Forget Quidco... As this is not a 'promotional' code, you should be entitled to cashback too. (possibly pay only £2.44)
Now down in price, to £5.24 for 100g of mushroom spawn