Thanks goes to Rastafari for bringing this to my attention in a separate thread but I personally think this needs highlighting separately as it is a fantastic deal.
£10 per month (and even got a £10 credit)
Please be aware that it may not work for everyone but a number of people have received this already.
Use the link provided which takes you to Three's online chat and see if they will give you a better deal.
I had been trying for a couple of years to get my previous plan down from £20 and increase my tethering from 12GB tethering.