Iirc we did have a thread about this on the old forum, but the Beeb has this article about the EU not accepting UK passports that are older than 10 years since Brexit.
Seems to be mainly people flying that are having problems.
Just checked hubby’s passport and his is 10 years and 1 month. 
So far no problems using it for the ferry. 
All the advantages of leaving the EU make up for this trifling inconvenience.
Oh wait, there have been no benefits to leaving 
This only applies to (visa-free) UK tourists.
It does not apply to UK citizens with a Schengen residence permit or visa (these only need a passport valid on the day of entry to be allowed to travel/enter, the expiry date or issue date are irrelevant).
Third-country nationals (non EU/EFTA), regardless of their visa obligation status, wishing to enter the Schengen Area for a short-term stay (without exercising a gainful occupation) not exceeding 90 days in any 180-day period must be in possession of a recognised travel document that meets both of the following two requirements:
The travel document is valid for at least three months after the intended date of departure from the Schengen Area; and
it was issued within the last 10 years (the date of issue only concerns entry into the Schengen Area).
The travel document’s date of issue is the determining factor, regardless of any decision made by the authorities to extend the period of validity.The two conditions mentioned above do not apply to travel documents of third-country nationals who hold a valid residence permit issued by a Schengen country, or to persons who were issued a valid category D visa for a long-term stay by a Schengen country (national visa, considered as equivalent to a residence permit). In such cases, the travel document must be valid at the time of entry and remain valid for the entire duration of the planned stay in Switzerland or in any other Schengen country.
I had an issue with this at Edinburgh Airport when I had 3 months left on my passport and I wasn’t sure easyJet were going to let me beyond the baggage self check in. They took my passport and residence permit away and we had to point out the conditions to them. It was a bit hairy as I had to wait 20 minutes for someone to come back and say it was OK for me to fly.
Why would he take the risk rather than just renewing his passport? It doesn’t make any sense to me.
It only takes one jobsworth border guard who decides to make life very difficult for you and your travel plans are severely disrupted.
Well, it’s okay to 2027 so he has some time before he needs to renew. 
Just something to try and remember if we’re still travelling by then.
Oh your first post wasn’t very clear. I understood it to mean he was still using it ten years and one month after issue so although the expiry date was still valid it was invalid due to the ten year issue date rule.
More travel woes for British Holiday makers entering the EU or Schengen area ( which includes Switzerland, Norway & Iceland ) ‘in the pipeline’ !!!
Countdown to ETIAS the new EU member states entry regulations for all ( Non EU citizen ) visitors & travellers entering the EU or Schengen area. Don’t worry this has been pushed back several times with the latest news being that it will be implemented & in force by mid 2025 nevertheless for those who plan at least a year ahead it’s worth bearing in mind these regulations.