The issue may be linked to the aerial you have, as it might just need a little bit of tweaking to get the correct reception levels right, or it may need to get replaced, if you can try and fiddle with the aerial then see of this works, the stronger the signal you get the better the Bravia TV and T2100 set top box will perform.
It turns out we have a dicey amplifier on the line from the aerial. It works if it is not disturbed. Unfortunately our Christmas tree had disturbed it. The tree is gone, the amplifier fixed in position and reception has resumed - except for TV3 etc when it rains.
Thanks for the help.