Just wondering if anyone can help or provide some suggestions, sorry long so cookie and alcohol for those who get to the end!

I have recently bought a veccy C, a week before i picked it up it developed a fault with opening by the key which the owner thought was the immobiliser. It didn't happen all the time but he put it into Vauxhall to have it checked out. Vauxhall couldn't find anything wrong and even plugged it in to see if it had any fault codes which it didn't. They replaced the battery in the key and left it at that.

Now i picked the car up today and on the drive home the stereo went off then came back on very quietly and i lost every single light, including brakes & indicators. After about 10 miles it all came back on again!

I was following my OH and had no way of signalling him to pull over to take a look at the time (forgot my mobby too! )

Anyway remainder of the journey remained problem free. Later in the afternoon we went out again and it did it again but for a shorter time frame. My OH thinks it may be linked to the main battery but i'm not so sure...

Has anyone ever experienced this before or have an inkling what it is?

It's a 1.8 VVTi SRi by the way.