42 gas turbine courses in the UK:
http://www.emagister.co.uk/gas_turbine_ ... 251687.htm
I suggest for your purposes (career development) you would be better off with a 4-day or 5-day short course, rather than self-study from a multimedia course. Of course that depends on how much you (or your employer) are willing to spend (typically £1000 to £2000 for a short course) and whether you can be released for a week.
You already have an advantage of practical knowledge of dealing with engines and parts; you have a lot of knowledge already and just need some theoretical explanations to put this knowledge into context and make it all make sense.