When these sets detect a dangerous situation - they power down and give out a signal via that flashing LED on where to start looking.
A 3 blink shutdown indication on the panel means : " X DC-DC Converter " is the troublesome item.
It is detecting an under or over current situation and shutting down to avoid further damage. Typically an IC on the XDrive has failed, and the suggestion is to change out the X Drive board in it's entirety.
Finding spares in the UK could prove to be difficult. Try eBay ?
Be sure the numbers match up exactly.
Perhaps a local technician might be able to get one for you - or even troubleshoot and replace the defective IC (s) on the X-Drive if you were to disassemble and take it to him - it wouldn't cost much.
Suspect ICs in this case would be IC3702, IC3712, IC3701, IC3702, IC3712, or even Q3122
Aside from swapping the board out - there's not an easy reset or procedure to get it up and working today. It will require repairs/parts replacement.
There is a slight chance there was a power anomalie, and you can try to release the power down status. Do the following before trying to repair:
Turn the main power switch on the TV to OFF - then unplug it from the mains for 10 minutes. The red LED should no longer be on.
Plug the TV in again at the wall - but do not turn it on - instead wait another 30 seconds... then switch the main power on. If the TV returns to standby - power it on as normal.
If the above does not work, it will require repairs.
If you have additional - Just Ask.