Presumably things have got worse now colder nights are here?

Could be a glow plug or two on the blink causing the intial misfire, they are usually linked by a heavy duty live wire so to test the current each one draws you will have to disconnect the link wire from each one and provide a live feed fed through an ammeter to each one individually, last time i checked glow plugs like this a healthy one drew some 15 amps but that was a good few years ago.

First of all though make sure there is power going to the glow plugs from the relay/timer when you switch the ignition on.

You could remove each glow plug and watch it physically glowing red, but i'd be inclined to leave them in place unless intending to replace.

Gurgling sound might be air in the heater matrix, try bleeding the heater outlet pipe to expel any air and see if things improve.

Glow plugs don’t do a lot on a common rail Diesel engine . They really only come into action if the ambient temperature is 5 degrees or less. I would suspect the injectors are in trouble. A leak off test is not really good enough. They need to be removed to do a flow and spray pattern assessment.

Thanks for all the replies. Yes the problem was the same at the height of summer so I am presuming not a glow plug issue too.

I tried some diesel additive hydra maximus (good stuff that turned it into premium plus plus apparently). Didnt change things.

I have a gut feeling it is injector linked. Could this make the gurgling sound? Will try and find somewhere that tests them.

Cheers

Heater is spot on, and no coolant leaks etc. It happens when I accelerate. Take foot off, and sound stops. Doesn't do it all the time. I'm very intrigued. Cheers