=> He came without clearing the customs, and without even knowing he needed to between UK and France.
He has probably not been outside the UK very much. Or he saw wrong airport data - easy to do.
=> His approach plates were completely outdated (year 2002) and he tried to convince me that those differences since then were "not really important".
This highlights lack of IFR (airways) experience. Very few pilots who are not aircraft owners fly airways, due to the difficulty in renting a suitable aircraft. And if you don't fly airways often, it is hard to justify getting Jeppview; European coverage is about Euro 1500. OK, one can get free plates from Eurocontrol or Olivia but not many people like those because they use some strange notation and are hard to read if printed on A5.
Plus a lot of training is done with old approach plates, because the schools won't pay for current ones. Before I got electronic data, I used to give away my old approach plates to schools; they used them for training.
=> He had no IR flight time endorsed in the logbook by any instructor (it is the second time we have that problem with a UK pilot... Why instructors do not endorse logbooks in UK? Is that normal on your side of the Channel ?)
This is normal. Instructors rarely sign individual lessons. When I started on my FAA PPL/IR/CPL route I went back to the old instructors and got them to sign everything possible.
Someone above proposed that approach minimums would be raised for private IR pilots (+200 on a precision, +250 on a non-precision, if I remember well).
I do not agree with that.
If your minima are raised, then you will probably more often go for a missed-approach, and performing several approaches is more dangerous than only one, because you get tired, nervous, etc.
Moreover, diverting is a really more hazardous thing than performing the approach to the legal minimums.
I agree. One should always fly to published minima. It is the safest thing. Unless the approach has gone badly wrong...