SORTED !!!

Strange how no matter how many thing are tried there is always one more to try... and finally the problem is found.

It is my BT Vision Sports CA Module card.  It is an old card from Setanta Sports used to unscramble the BT Sports channels provided thru the BT Vision box.

Simply removing the card when the problem with HD channel tuning arises brings all the channels back perfectly, putting it back has no effect until the TV set is switched into standby, as explained in my original post.

So, if anybody else has this problem with this configuration try this solution.

One more thing... if anybody has a "direct line" to someone in Sony, not Customer Services please, who would need to know about this problem with their TVs please let me know.