Can one of you experts please tell me why sometimes the picture on my new TV freezes for about a second or a section of it breaks up into small squares?
generally because they're trying to squeeze a quart into a pint pot.
Digital channels are grouped into multiplexes of rstricted capacity - there is isn't enough bandwidth for each channel. They get around this by adjusting the bandwidth for each channel on the fly - a channel with a relatively static display with a low update rate - a discussion programme etc - with give up bandwidth to something with rapid motion like a football match.
Sometimes they get it wrong, sometimes they just run out of bandwidth - which is when you pixelation/stuttering of your picture.
The solution is more bandwidth when the analogue frequencies get shut down. But, seeing as how much money the government auctions them off for, the buyers will try to fit in as much as possible.
I am not sure, even after the success of the recent trial, if freeview/FTA HD channels will ever happen. I would imagine that HD will remain restricted to those willing to pay for the quality/bandwidth, and the remaining bandwidth will fill up with more channels.