I'm currently doing there residential course. Smith is right as far as requirements go. My understanding is you don't need a class one to commence the course, although Im sure they would definately recommend it.
Just found an email I received from GCNS before I started...
<quote gcns>
2. You require to have been educated to at least Standard Grade or GCSE 'O' Level in Mathematics and Physics, + hold a JAA or ICAO PPL. Multi-choice mathematics and physics papers are alternatively available on request.
3. There is no formal selection process although places are normally limited on the courses to 15 persons, thus allowing for a more personalised approach. Please note that due the courses being small compared to most other places unconditional places can only be offered on receipt of a completed application form together with a non returnable deposit of £xxx (cheques made payable to the Glasgow College of Nautical Studies).
</quote>