Bit out of date here, but once upon a time I worked for Seaward designing some of their test gear, so:
1) The IET/IEE guide is excellent.
2) No matter what various documents imply the leglislation does not specify that electrical devices need to be PAT tested (I hate that repeat testing-tested). All PAT testing does is provide evidence of care/maintenence should something go wrong.
3) (possibly out of date bit) There is no need for qualifications to do PAT tetsing, but how do you demonstrate competence without them? Your prospective customers/employers may impose a minimum qualification though.
4) Is this going to be your main line of business? If so you need to remember that your competitors will be looking at about 2 minutes per test. The bigger machines have more ability in generating high currents for the earth bond tests, which the hand held machines will struggle with (this is a bit market driven, earth bond tests tend to be lower current in IT kit, and other tests tend to cover the same ground). The point here is testing duty cycle and £ in your pocket.
5) If you are in an industry where you cannot bypass the big earth bond tests (ie non IT) then you may want to look at getting a couple of big testers, so that one can cool down whilst the other works.
6) If it is going to be your main line of work, then the device above does not seem to have anyway of downloading the results to a PC. When you do a repeat visit to a site, it will greatly speed up the tests if can import./export data on each result. This also makes H&S managers happy cos they can then look for degradation in a the results.
7) Seaward (and others) do a range of kit that will read/print bar codes. So if you return to a site, you can just read the label you prepared last time and your machine will reapeat the same suite of tests.
All in all it is a bit of a racket. H&S bods generally want a bit of paper saying that they wwill not go to jail. Testers want to get through as many tests as they can, cos they get paid per test, and generally, nothing goes wrong ....
9) I may sound a bit cynical about it being a racket, but read the IEE/IET document and the bit on the visual inspection. Now imagine yourself in a call centre crawling across the floor checking leads, looking for twisted cores, wires loose in the plug, fuse in the plug matching the rating of the appliance, then wonder how the big contractors are budgeting on about two minutes an appliance...
I'm sure more will come to me - 10 years since I was there ...and it has taken me a while to remember all this, so if some one has posted all this in the mean-time