Thanks to claire21 - MSE
'the flyer says N136 code gives free seeds with every order worth up to £5.99 but it works on £40 sets of seeds, £20 peas and planters etc.
Just add a cheap product to your basket, then expensive seeds - just type in seeds to search then high to low. Add code at basket and seeds should be free - free P&P is auto at the moment, so just your cheap purchase to pay for.'
EDIT - you can delete the cheapest seeds and get the item for free. no payment details taken.
the link should take you to the seeds search page; with all results from highest to lowest price.
i ordered the £40 seeds for my mum; which she will love!