Does anyone know why for no apparent reason the overall total mileage on my display ocassionall starts flashing/blinking?

It is nothing to do with low fuel level or a low temperature.

You need to have the car plugged into diagnostics and have a Proxy alignment done on it - effectively putting all of the timing clocks in the CAN modules back into sync.

OK, thanks, but what does that actually mean?

Is it something I should get done ASAP? What will happen if I leave it, as I have noticed this a long time ago but it happens so infrequently that I forget about it.

It's not urgently required, as far as I know. The usual cause is that the battery has been allowed to go flat, or been disconnected for some time..

Basically, all of the car's control units use a common bus to communicate, but in order to do so without clashing with each other, they much be using a common timing cycle. A proxy alignment procedure basically tells them all: 'listen, I'm going to tell you when you can talk, and when you can't'..

Ok, thanks. Strange as I have never had any battery problems.

I had this occasionally but again had no battery issues. Didn't seem to do any harm.