HURRAH, a result.
The problem was at my local exchange.
Now I have a perfectly good TV picture on sport 1.
My advice is: DON'T give up complaining!
Thanks to those who have tried to help me.
I am having the same problem with live football on bt sport. Checks on my line and exchange are coming back as being ok. Tried adding RAM and using a RJ11 cable from hub to main socket without a filter. Next is to get graphic card checked, and if that fails it leaves the processor.