You probably didn't know you needed one.
I'm actually looking for a QL-720NW (as it's got wireless, and is about £50-60 by claiming the £50 cashback) but stumbled upon this deal.
It's an older model, but might be okay for some people. Seems to be around £40-50 in most shops, but £29.99 at Ryman with £20 off. You can use NEW2 code if you are a new customer to get £5 off, and free delivery if you spend over £30, so you need to add the cheapest item you can find to tip over the £30 needed.
Cheapest item I can find is a 49p pen.