PD
Because I have experience of teaching students in 21 days and in much longer periods. The 21 days was an extension of MOD flying scholarships. The RAF would not dream of trying to cover the content of a PPL in 21 days, their equivalent the old BFTS took 6 weeks.
CD
" Do you honestly think the CAA/JAA would issue licenses without a UK "checkride" for US trained PPL if that was the case?"
They don't, if you want to convert a licence you have to take a Skill Test. If you fly on the foreign licence then the CAA are merely complying with an ICAO agreement. If you mean the US trained JAA licence then the examiner is a UK authorised examiner however, he works for the company selling the product!
Since writing my last post I have spoken to another CFI who complained
that he had encountered yet more US trained pilots who cant work the radio, and need a further 10 or so hours.
Ask arround at a few schools, its quite common. There are always a few who don't need any additional training, but the majority do!
Not many potential students know that a US Instructor does not have to attend an Instructor Course like their European counterparts. As a result, the methods of instruction vary widely.
I would not wish to deter anyone from learning in the US, I have flown with many people who have, some very good, some terrible but the main point is that experience tells me you can't produce many good pilots in 21 days!