The last time I needed parts the MAIN parts centre for Honda was Holland

No - It's Ghent in Belgium, has been for years.

Sounds like it could be a similar issue as mine was then, with a pandemic twist and a specific issue with an unreliable OEM part/system. Quite a lot of the EU-wide parts depots appear to be located in Belgium, perhaps because it's quite central.

And still waiting.

Has the dealership/garage given you any idea as to when the part is now due to arrive? It could be just as much the logistics of trucking the part to the UK from the continent and even (if it is made in Japan) similar issues with shipping/flights, etc.

One of the big problems of the last 6 months has been the 'pingdemic' - more than people actually being sick and off work with COVID, but having (sometimes needlessly, others not) to self-isolate, which if that's lots of factory floor or HGV staff can obviously lead to significant delays in the manufacture and distribution of goods - whether Hondas, Audis or anything else.

I presume the rest of the car works ok, so you may be somewhat fortunate, especially as the weather in the UK isn't exactly 'hot' at the moment, thus needing A/C is less of an issue.