Ok, after three engineers this problem 'seems' fixed. There was a couple of blocking moments during a Channel 4 HD programme Sunday night but that could just be coincidental random glitches and generally everything seems better.
The engineer said that the problem was that there was way too much signal coming through to my house. A network engineer had to go to the relay box up the road and did something to slow the signal from there. Normal attenuators screwed onto the back of my Tivo and in my external brown box didn't work - so that was why something had to be done by the network guy to the relay up the road. Anyway - as I say, things seem to be working ok at the moment. Hope that helps some of you guys with the problem too.
The engineer said that the problem was that there was way too much signal coming through to my house. A network engineer had to go to the relay box up the road and did something to slow the signal from there. Normal attenuators screwed onto the back of my Tivo and in my external brown box didn't work - so that was why something had to be done by the network guy to the relay up the road. Anyway - as I say, things seem to be working ok at the moment. Hope that helps some of you guys with the problem too.