Thanks to all of you who responded. I can only provide part answers, and at 85 am not brilliant on technical matters. I can definitely confirm using a new HDMI lead did not help. I am not too sure if any of what I watch is in SD, as most are HD. Using a different HDMI port does not seem possible as the Virgin box is connected via one piece of equipment along with other leads (speakers, DVD, Cd), but all connections were checked by the last engineer, who fitted a replacement box which cured the actual connection problem, but the occasional blackouts have continued.