Ok if it might be of use to anyone. I've spoken today to an immigration advisor, and she is insistent that these written criteria must be followed to the letter.

This means, you MUST have in your letter from your employer(s) your type of contract, how long you've worked there and what your yearly salary is.

If you cannot give a fixed yearly salary - this will cause your visa application to be rejected. Never mind if you earn half a million a year, it will be rejected and she has seen recently one such rejection.

So many workers in the NHS, restaurants, offshore ship workers - you can't have a visa.