Hi Mike, I have just become an employee after years of being self employed. I had some good years at being self employed, mind you never making as much money as people/friends think you are! Basically making a decent living with the perk (if it is one) of working for yourself.
I would probably still be self employed if it wasn't for a visit/inspection from the tax man. I had an inspection/investigation that went on for two years and it completly wasted me both mentally and financially. I am still very, very bitter about it because I am not a dishonest person and it was peanuts the money I was allegedly taking out of the business. They threaten you with a more in depth and much longer lasting investigation if you don't pay there demand.
That was it for me, I think it's hard enough as it is running your own business without these b******s raiding your bank account/savings.
I closed my garage at the end of August, paid the lad who worked for me his redundency and had a couple of months off.
I did some mobile work during November which I enjoyed mainly because the weather was kind and I did make good money that month as I had no overheads to worry about!
I was offered a job starting in December, although it's a 20 mile drive through some pretty grim traffic morning and night I am enjoying it. I start at 8.30, finish at 5.00 Monday to Friday and switch off when I leave the premises, no sleepless nights, no hours of paperwork etc, etc.
The bottom line is I don't think I would have my own business again, not with premises anyway. When I closed my garage I was looking for a small place were one man could comfortably work but of course I wanted it in a decent area and relatively cheap.........nigh on impossible to find.
My prefered option if this new job fails (I hope not) for whatever reason would be going mobile again, I did it from a small corsa van which was a struggle so I would immediately invest in a bigger van.
There are seemingly a never ending row of hoops for garage owners to jump through these days, new legistration with obvious cost implications!
In my opinion the cost of buying/renting your premises added to your other costs like insurance, rates and one of the biggest ones, tools/diagnostic equipment etc. makes it very difficult to make a reasonable living. I personally think the only people making money are either small "one man bands" in inexpensive premises, mobile (sevicing and also the diagnostic specialists) and the big workshops that have several mechanics working but obviously these need to be kept busy all day!
Sorry for rambling on just thought I would share my experience.
Cheers,
John.

PS My best advice is re-train as a joiner, plumber or an electrician etc, you'll need a beat-up van, a bag of tools and a surly attitude.
Don't worry though you'll make loads of money