I don't know if offers are account-specific or targeted, but if I login, I can see about 6 voucher offers, including for example:
1) 2 vouchers each for £2 off a £20 spend - at a price of £1.99
2) in 6 days, I can apparently buy 2 vouchers: £1 off a £15 spend and £1 off a £25 spend - at a price...