2015 Vauxhall Astra engine keeps cutting out

Go back to the vendor,
Clearly you have an intermittent electrical fault.
If it something as simple as a faulty crank angle sensor it wouldn't show up as a fault code because all the engine ECU "sees" is no signal and assumes the key has been turned off.

Thankyou very much

But all the lights and touch screen stay on no warning lights and brakes still work, would the garage not know to check what you suggested? I will take your response to them, thankyou

That's the problem with electrical faults you can spend an awful lot of time finding the fault.
and usually after sometimes days it can take just min's to fix.
And it doesn't help your technicians when the dam fault doesn't present when they're looking for it.
Frustrating or some other word that begins with F.

Hahaha! I too can think of a few words beginning with expletive! I want to give the car back and get my money back, unfortunately as it's after 6 months (just) I now have to prove that the fault was there upon purchase....🙄 Happy days...

Have you had a look at this similar problem:

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my astra dti cut out several times with two garages failing to find the problem, it then went to a diesel specialist who found it to be a rev sensor problem which was replaced and had no problems for two years now. hope that helps with anyone with a similar poblem