Rang up Sky to make changes to my TV and been told that they are currently having a promotion where Sky mobile sims are half price. I ordered Unlimited minutes, Texts and 3Gb data for £7.50. Because you get Sky Go extra included free which I currently pay for I'm effectively getting the 3gb sim for £2.50 per month. This is a contract for 12 months. They use o2 and I like the idea of data rollover.
Also been advised that if I cancel my TV, then the minutes and texts would remain. If your a Sky TV customer then it may be worth giving them a call.