Hi and welcome to Just Answer.
what type of driving do you do short journeys long journeys ?
any warning lights appear when this occurs?
what I believe is that the ECU is triggering a diesel particulate filter regeneration I have come across this once before .
I would not say it is an engine management fault as such but there should be a software upgrade that can fix this but you will need to have a Vauxhall dealer do this for you.
If you need any more help with this them feel free to ask.
Hi Rob. Thanks for your prompt reply. I will speak to my local dealer. I'll let you know how I get on. Thanks for your help. Paul
I will look forward to your report.