Well' I got up this morning not looking forward to working out in the snow knowing that I would be wasting my time and Its probably time to look for another vehicle, but it's worth one last try.
Removing the banjo bolt was easy enough.
And there pressed into the bottom I could see a brass insert, this is a tight fit and impossible to remove.
I could get air to flow through it by sucking on the end but there was some resistance.
So I put it in some petrol and tapped both ends, initially no debris came out.......then slowly very very fine particles started to appear.
Now I could suck air through it very easily !
Starting after reassembly the first unusual thing that happened was the management light extinguished immediately, normally after changing the filter it would take a few cycles of driving before it would happen.
So , although i don't like to tempt fate, I do believe this has been the fault all along. And a fresh filter ( and loosening the fuller cap, will try tighening this now) was previously just offering a little less resistance to fuel flowing through the partially blocked banjo until it was blocked almost totally.
This fault has plagued me for over 50k miles and 6 years of ownership , and one expensive visit to a diesel specialist, who could not replicate the fault !
Thank you for everyone's input .
I just might try the lottery tonight !

There's a big distinction between manual parking brakes operating pads via dual purpose rear calipers (which are prone to losing grip when cooling), and the more expensive and more effective design of drum inside disc parking brakes, indeed i'd suggest a traditional rear drum brake operating the same shoes for both foot and parking brake is more than adequate for most vehicles, and provides a much better handbrake to boot not affected anywhere near the same by heat contraction.

The only downside IMO to rear drum brakes is that they get even less inspection by the current farce called servicing, and when shoe replacements are required its a bit of a faff on some (not helped by the trend to build the drum and bearing carrier into one hub unit, kerching), however generally rear brake shoes last nigh on 100k miles and often enough rear drums never need replacement in the life of a vehicle...but they don't impress the impressionable so discs it is whether needed or not.

Ford had a look yesterday (gave me a 15 plate Fiesta as a courtesy car with 3 miles to empty worth of fuel in it....) and said they checked all tyre pressures and reset the TPMS via the IDS system.

Will see how it goes - thanks for the responses.

Glad to see that (eventually !) it seems to be getting sorted. Pain in the backside that it has been, unfortunately, such a long-winded process to get there.

You may find that the dealer is on Trustpilot or another such review site. As such, you may be able to leave a review for them on there. I'm aware that HJ doesn't allow poor reviews like this on dealerships - understandably, as there is too much potential for false reviews to be left, and websites can be held responsible for those, in law....

There are only two things which will normally cause a bulb to fail, one is over voltage, in which case it should affect the other bulbs, or excessive vibration, otherwise as already suggested poor quality bulbs.

I usually use 'Ring' bulbs from Ebay, pretty cheap and no problems.