Instructor requirement for training flight (revalidation by experience)

[Zonkor]

I might be in a little pickle regarding my revalidation by experience and am Looking for some guidance by somebody experienced with the CAA ...

Before my UK CAA-issued EASA PPL (SEP) was to expire, I dutifully sent off the requested documents (CAA form SRG1119B, original logbook, certified copy of my license) to Gatwick for a revalidation by experience. (I don't live in the UK, so that's my only "simple" way of doing a revalidation by experience.)

A few weeks later (already after expiration date), I got an email requesting the license of the instructor that I did the 1h training flight with. I'm told (yet to be confirmed) that the instructor might not have an EASA instructor license, but merely a French national instructor license.

Edit: I also have a still-valid TMP class rating with my PPL, if that's of any help in getting the SEP renewed.

As I smell trouble, I want to ask:

1. What's the requirement for the instructor giving the 1h training flight? Does she/he have to be an EASA instructor? (The instructor is with a French flight school that's well-known for mountain and glacier flying instruction.)

2. Can I fly while my license extension application is pending?

3. What if the CAA indeed won't accept my training flight, and my license indeed expired? How can I revalidate (renew?) it? Can I do it abroad, or do I have to go to the UK?

4. Is there a chance that the CAA grants an exception in such a case of hardship / pure formality? For instance, I could do the one-hour training flight with an EASA instructor asap (license only lapsed since a few days) and don't have to do the full-blown renewal?

Thanks a lot!

Michael