France accepts UK sub-ICAO licences and medical declarations

You need to ask UK CAA or LAA as France is just accepting what is accepted in the UK.
If you can’t fly a G reg.certified on a self declaration in the UK,.then you can’t in France.
A French pilot needs a Class2 medical to fly experimental in French airspace.

There are two aspects here:

• the UK is supporting the PMD (currently for uncertified only I think, but this changes every 2 weeks, and it is widely expected that very soon the UK will merge all this crap together and it will be “PMD-for-all” within the UK)

• France accepted it

so both countries think it is ok to do that. Well, it’s been proven over many years that the Class 2 has near-zero predictive value, so this is good, but why only in an RV (etc) and not in say a PA28?

What is the rationale?

You can’t “ask the CAA” because there is nobody there with a brain answering emails or phone calls, and you can’t “ask the LAA” because there is nobody there (I am told they all have full time jobs)

I"m sure the LAA has full-time staff. Maybe without the authority/knowledge to answer that.
The CAA received a paper question from me on 16/11/21 and it was immediately scanned and emailed to the appropriate person, who emailed the reply on 29/3/22.

Worth a mention that the French acceptance in this thread is split into two:

One is a permit aircraft that fits well-defined historic criteria on design and end of production. (Actual dates, see LAA TL.2.08).

The other is to do with being ‘amateur built’ permit aircraft, and factory-built permit aircraft are not included.

LAA leaflet tl.2.08 is below. go to the sub heading ‘France’:
TL_2_08_Travelling_abroad_in_a_Permit_Aircraft_pdf