Good advice from Bunbry - it's very hard to make money writing, particularly if you're determined to write what you love writing, and not to stick to a known commercial path. The average member of the Society of Authors - which is the nearest we have to a trade union - earns less than £10,000 a year from their writing. But it is a wonderful thing to do...
On courses, I've heard mixed things of Writers' Bureau, to be honest.
WriteWords does some one-to-one courses - click the tab above.
You could also ask at your local FE or HE college - most of them have some Creative Writing or Professional Writing classes.
These are free, from the Open University, which would be a good way of dipping your toe in the water:
and the OU also have more substantial courses which are paid-for. Then there's the Open College of the Arts: http://www.oca-uk.com/courses/writing-courses.html
which has several levels of course as well. Exeter and Oxford Universities also have online courses.
These might be worth a look - I can't say I know much about them, but Writing Magazine is very long-established, and I do recognise some of the tutors: https://www.writers-online.co.uk/Home-Study/
One option, if you hesitate to commit to a course, would be to get hold of the absolutely brilliant book Creative Writing, a workbook with readings, by Linda Anderson. It's the textbook for the OU course that I teach, A215, and it's the best structured and most comprehensive one I know, and anyone who worked through it - even without being on the course itself - would learn a vast amount.