This is an overview written in answer to an email. I'm publishing it via the Horse's Mouth as it might be useful to others. Please bear in mind there are a lot of subjects that I have NOT touched on here such as the need to obtain an appropriate visa if, like my correspondent, you're not an EU citizen.
Typically, trainers in the UK are contractors, just like in the US; I worked in that way for about five years but it's a while back - indeed our current company - Well House Consultants Ltd- was set up as the administrative mechanism for that, but grew into a complete training provider with our own training center, etc. ((Note - changes in UK Tax law and something called IR35 men that initial setup advise would differ today))
There's a great tendency in the UK for courses to be advertised, but only run if there's enough delegates booked. For the contractor who's booked to give the courses, a last minute cancellation can mean a sudden vacant week with no income unless you have alternative non-time-critical work ("another string to the bow") such as web application programming with which to fill in.
Your field is, indeed, roughly the same as mine but not similar enough for me to realistically give you the sort of rates you might charge and the job market state. I will comment (although I'm sure you realise already) that the whole cost of living metrics in the UK differ greatly from those in the US, and when doing your sums there's much more to look at than just income.
Yes, you will find authorised training centers/courses over here ... they're a great way for the Microsofts and Novells to control the level of training that's given, to ensure there's appropriate sales pitches made on each course, and to syphon off some of the delegate's income. We've been invited to join some such schemes, but we've declined to do so after careful consideration. It does mean we're responsible for obtaining or writing our own material which for the niches we're in suits us well.
Much work is obtained through word of mouth / knowing people. One or two good contacts might be all you need to get started, but it can be a slow process building up and I rather suspect that by the time you're running on an economic footing, it might be time to go back to the USA when your partner has his visa. I've not come across too many listing agencies.
In the UK, you'll also find a lot of training resellers who match up training requirements to training organisations - middle men. We ourselves aren't keen on dealing with them - they typically request (or demand) a heavy fee from the trainer, they're a lot more hassle to set up and won't let you speak with the client to find out what he really needs from his course ahead of time, and they're slow payers. However, they may provide you with an "in". In a diverse world such as training, some big companies will use a single reseller to bring together all their training needs so that they (the big company) doesn't have to do a huge amount of research itself and can go to a single, all be it indirect, source.
Area wise ... you might find something in London (which you mention), but high tech stuff is spread all over the UK. In our own niche fields, we have a training centre that has access that's as reasonable as anywhere, but we have to be prepared to travel too. I was in Cambridge late last month, and I'm in Liverpool in a couple of weeks for example. In our particular fields, there's occasional opportunities further afield - I was in Saudi Arabia a couple of weeks back, and I'm in Ireland later this month. (written 2006-06-08)
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