Instructions:I've used these guys a bit, they've been excellent. This is copied from the email they sent me:
You know how we work, there are no hidden pieces of small print, it's simple. The £4 voucher can be used against any purchase between now and Wednesday 27th January at 1pm so you better be quick!
The £4 voucher below can be used 5 times this week.
To claim your £4 simply enter MC458X88 at the checkout.
Don't forget, you can even order now and request a delivery date in the future, and all gifts include a free personalised greetings card.