Well after a few days of waiting for the BT Vision team to get back to me I decided to ring them on Monday 22nd April.
Spoke to a nice young lady who read all my details and what problems I'd been having. She suggested that they should send me a new Youview box and see if that cures our problems. I was a bit sceptical but said OK, she said if it didn't solve anything they would start looking at the exchange to see if they could locate any faults there.
The new box arrived on Friday the 26th April, and as I had a few recordings to watch I decided to swap it over the weekend. That night we watched a Criminal Minds and it did it's usual, picture distortion, sound going off and then after about 12 minutes it stopped and went straight to the menu that appears when a program has finished...nice. I restarted the program fastforwarded to where we were and it started with the sound problem but this time it went off for about 30 seconds then back for 30 seconds, then off for 30 seconds...........you get the picture. So I decided to swap the box.
It took around 15 - 20 minutes to swap the box over, went straight to the program again and oh my god! The difference was amazing!! The sound was crisper, the picture was much sharper and much better colours. The most amazing thing was that the program started instantly. I tried a few other programs and they all started instantly, watched 4 episodes of Criminal Minds back to back and no problems what so ever! fantastic!
With the old box programs were taking as long as 3 minutes to start! Also the Youview menu is now pretty much instant, I can scroll through it quickly and it doesn't have to wait ages for the menu to catch up anymore.
I'm going to watch nothing but on demand movies and programs all weekend to make sure I'm not dreaming but I'm pretty confident that all my problems have been cured with a new box. Great stuff BT Vision team.
One complaint, Criminal Minds series 4, episode 2 gives an error code of BTV162 and just won't play which I now no is a server error, probably file corruption so hopefully will tell them when I ring up Monday so they can sort it.