Thanks to David_Bn, who last week booked an Engineer to look at this and he arrived the following morning! Thanks David.
He was very helpful and thorough and did find a problem. After the signal came into the house on the main cable it was very poor. He changed the white box on the wall and whatever is in it and also the splitter that splits signal to broadband router and TV 360 box.
Over the past week there has been a 90% improvement, but occasionally some recordings still do it. It's not enough to justify calling an engineer out again, so I'm happy.