I contacted Panasonic customer service who were very helpful.
First they got me to disconnect all devices, including the aerial and then the power. Leave it for 2 mins before reconnecting everything and power it back on.
Interestingly this obviously did something because the sound was horribly tinny when the TV came back up.
When I mentioned this the CustSvc guy had me run a Factory Reset. Which took it back to out of the box and I had to run through the entire set up process from selecting the language.
I now have a working EPG and a quite different looking apps view when I press the Home button.
They also sent me an email with info they want if I have issues again. These are:
.Serial Number
.Current firmware version on the unit
.The transmitter you receive from
.Picture of guide issue
.Video for the issue

For now the TV has a stay of execution. Time will tell ....