at one point my pronounciation was nearly perfect.
I'm impressed! I have only met one Pole who spoke English with no discernible accent.
It clearly means I must have come to the British capital with Received Pronounciation already on hand.
The only thing I will say, is that those English people who do speak with an RP accent, are usually those who come from monied backgrounds and attended public school. However as far as pronunciation goes, I'm sure you spoke very clearly indeed :)
that TV course which later on resulted in almost every person in England being sincerely amazed that one was able to acquire RP to such an extend in living outside England or an English family.
It sounds like it was an excellent course, I didn't realise it was so in depth, but of course, a lot would also depend on the learner and their natural aptitude etc.
English is particularly difficult to learn as far as the proper pronounciation of vowels and diphtongs is concerned.
I would agree with that. Too often I hear Poles pronouncing English 'u' as 'a' for example. Mug is often pronounced as sounding like Mag. I'm sure I make the same sorts of mistakes in Polish though.
Natural syllabic stress (NSS) is in my view the most difficult thing to achieve by a foreign learner of English.
Yes, there is no substitute for spending time in a country and listening to English speakers every day. The parts of words which are stressed In English are different to those stressed in Polish.
I hope she was right, but years ago when I was learning how to pronounce ' szczęśliwa', my friend's daughter corrected me by saying I was stressing the 'sz' at the beginning of the word, when I should have been stressing the 'cz' instead.
NSS is no longer present in my English and in addition to that my fluency has deteriorated significantly, but this I believe is quite normal when you don't use the spoken language
They do say, if you don't use it you lose it, and unfortunately this is true :(
Your written English is very good though, so if you can write as well as you do, you might still be more fluent than you think!
Maybe you should come back to the UK for another extended holiday to catch up!