Moneysavingexpert site has a limited (10,000) number of codes which give new Sky customers 40% off for 12 months. You can therefore get the standard definition Sky sports/F1 package for £27.60/month (normally £46/month) or HD for £39.75/month (normally £62.75/month). Both packages have £10 installation fee.
This has tipped the balance for me and I’m finally going to get Sky for F1 this year!