Recently had problems with the picture repeatedly freezing briefly while watching the BBC via Freeview. If I switch to watching the 'same' channel via satellite there is no problem. Is it most likely to be the Panasonic or the Freeview signal? Anything I can do about it?

Mine has also been doing this (not very often though) - freezing while watching the freeview on it, then it displays a lilacy colour screen. I just been turning it off and leaving it for a while

If it affects BBC1, then it should affect all the channels listed under Multiplex 1 in the list [ First blue box at the top of this page :]http://www.dtg.org.uk/retailer/dtt_channels.html

... and if so it is a reception problem. Check your aerial installation and that your local transmitter is not on reduced power for any reason.

If only BBC1 is affected then you have corruption in the system and need to clean it out with a power reset.
Disconnect from the mains for 5 or 10 minutes.

It would do no harm to do a power reset no matter what the cause.
It is known that corrupt data can lie around and clog up memory buffers.