Loz,
I've been entertaining similar sorts of ideas for a while now.
To get into chauffeuring, WITHOUT DOUBT....you will need to pass the IAM (Institute of Advanced Motoring) Certificate. All chauffeurs advertise when they have it, consequently those who don't won't get used.
Also, you'll need to take some kind of course. There are many out there (PM me if you want me to point you to some websites). The important thing to remember is that the sort of market you are aiming for (the upper class market) will have used chauffeurs before, and so they expect certain things as standard. You really need to learn what these "certain things" are. Simple things like if you hold your hand out for a lady to help her out the car, you must always turn your head towards the front of the car over the door (so you dont look up her skirt......or rather, so she does not feel intimidated). I used this as an example, but the point I'm trying to get across is that little things like that will be expected AS A MINIMUM with the sort of clientel you're after.
So......to re-cap.......
Get IAM Certificate (easy enough)
Do recognised Chauffeur Training course (some places do "taster" days to see if you'll like it)
And then take it from there. Don't go buying an LS430 just yet, as one thing you may come to realise is the hours will be terrible and you may not like it. You'll be taking people to Operas, meetings, theatre, dinner.......all these things that normally happen OUTSIDE a normal 9-5 job.
Hope that's all been of help
Tony