Ofcom have a voluntary code of practice for broadband providers which Sky has signed up to. This means you're given an estimate of the average broadband speed you will receive before you sign up and a minimum performance guarantee, which entitles you to cancel your contract if a firm is unable to resolve your issue within 30-days without paying a penalty.
For added peace of mind, Sky offers customers the option to add Sky's Broadband Boost for £5 a month. This service will mean your line is regularly monitored for problems, with priority engineer service and Sky's Wi-Fi Guarantee, which ensures you receive strong broadband signals throughout your house or you receive compensation.