Heading back to Britain from Ireland last year, we (my partner & I in a 2002 British Registered Land Rover Defender fitted out for camping and looking pretty respectable) were stopped at Fishguard docks and asked for our (British) passports by the police. Fair enough...
Then, because both of us do Humanitarian Aid work and have lots of visas in our passports, we were asked for Work ID cards!!!
So, apparently, now if you are British then you have to prove that you are in work before you can re-enter the country on your British Passport! Interesting...
As it was, we had Work ID cards with us so we were allowed to proceed after checking - but it's the first time I've had to produce evidence of being in employment to get into a country - and it was especially surprising when it was to get back to my official place of residence!
Travellers with interesting visas in their passports - beware!
And Fishguard is the relaxed dock - Pembroke is much more grief for travellers to & from Southern Ireland
Of course, going into Ireland the Shengen rules apply, no passport checks, no bother - a proper civilised European country!