One little bit of advice, from somebody who has been in business since 1978, is that the people who don't pay are well used to threats. Their whole life is full of receiving threats of legal action and they just don't care. They know that most people won't carry it through.
My approach is to write to the Company Secretary or the proprietor if not Ltd (if name is not easy to find, phone them up and ask for his name, and if they say Why just say,
with a totally deadpan manner like you do this every day, that you are applying to have their company wound up / are applying for the proprietor's bankrupcy). Then say Thank you and end the call. That will make the person taking the call !!!!! themselves, and suitable pressure tends to be applied from within.
Then write a letter address to the co. secy or the proprietor, sent Special Delivery, saying that they have 14 days to pay otherwise you are going for a CCJ. Use the words "CCJ" abbreviated because that makes it sound like you do this all the time.
99% of the time this works. I have had to actually do legal stuff a few times in 34 years.
Must not worry about upsetting them - anybody who lives in this way is getting this crap all day long, and doesn't care. Decent people do care of course but aviation has less than its fair share of those
