I took car to a new garage
Car still has codes for misfire on cylinder 6 and 8 (originally was 5,6 and 8)
I know coils were definitely replaced by previous garage as I asked garage to leave covers off engine and I can see new coils on 5,6 and 8
Makes me wonder if original coils were fine after all (despite the first garage telling me they needed replacing)
To recap, plugs are all new
Today garage reset engine management light and at idle no faults came up (live test)
Need to bring car back for garage to investigate further