Gavin........Get yourself one of those Kewtech locking off devices. They are only made of plastic and feel abit cheap but I have not come across a MCB or main swith they wouldn't lock off.
I too had trouble with my Metrel Eurotester having to zero the leads all the time. So I use my old Robin 1620 for continuety tests now and the metrel for everything else.
I don't know where N.Notts Collage is but Chesterfield Tech. does a 2391 couse that I found good ( and passed ). There was only 4 of us on the course which probably helped.
I've got a Robin kts1620 and found it very easy to use (with no instructions).
Recently found out that it's the same as a Kewtech kt62 (I think thats the no.) and you can download the instructions from their website.
According to to them it wont trip all rcd's if you carry out the measurement...