jj...you don't gave to spend the vouchers *now*...they don't usually have a use by date...and if they do, it's a year.
You'd certainly need food in the future.
I would also love £150 of M&S vouchers, they last as said for 2 years and you can use on food, clothes, cosmetics, homeware. Surely you would get pleasure and value from that over the year?
Can you buy something with the gift card and get a receipt and then return the item and get a cash refund. Don't know as I don't shop a Marks. Daughter always gets £150 Marks vouchers off her boss at Christmas and she uses it for food in January.
"If any item purchased with a gift card or e-gift card is subsequently exchanged for an item of a lower price or refunded, any money owing will be added to the remaining balance on the card."