Just an update on the original problem. I held both buttons on the infotainment screen down for 10 secs to get a restart. When I came to the car this morning the infotainment worked fine. I have driven it all day, with many start/stops and the car left for 30 mins or more each time. Every time I returned the infotainment came on perfectly. Looks like it's sorted! It even told me I had a low tyre pressure!
Many thanks to the forum members for the tips.
Cheers,