Might be a voucher for free delivery if anyone can find it .
For free delivery:
Add plants to your basket,
then change the URL to http://www.thompson-morgan.com/gwm.
Go back to your basket and the delivery will be free. Of course, you can add the GW offers as well if you want, but you don't have to, to get the free delivery!!
This won't work if you use a voucher.
Topcashback is 12% . Exit from T&M and then return there via TCB to make sure of the cashback.