I'm afraid this isn't quite as good as getting 1 soup for Free, but CoventGardenSoups are offering £1 off when you buy 2 soups.
Several supermarkets are offering the soups (normally £2.35) for 1/2 price or less.
Therefore, buy 2 soups for £1 each and use the £1 voucher to get 2 soups for a £1!
To get the voucher, register your email via the link then print it off. (Yes the application they require you to download to print the voucher is perfectly safe)
ASDA: 2 for £0.96 with Voucher and offer
Sainsburys: 2 for £1 with Voucher and offer
Waitrose: 2 for £1 with Voucher and offer
Ocado: 2 for £1.20 with Voucher and offer
Iceland: 2 for £2 with Voucher and offer
Morrisons: 2 for £3 with Voucher (no offer)
Tesco: 2 for £3.35 with Voucher (no offer)