Thanks for the info.
I spent an hour or so reading through old posts on tappet adjustments. As with many things there were a lot of different answers. Some saying it's an easy job, to others saying it's quite difficult. Some saying they've never adjusted them without ill effect and others saying the engine runs so much better when they're adjusted.
As a maintenance procedure that costs next to nothing (if you do it yourself) I think I will wait until the Summer and have a go when I've got a whole afternoon spare.
If it ain't broke, don't fix it - jobs on cars can easily turn into a nightmare if you damage something while trying to fix something that was never broke in the first place - and you may well disturb something that causes you a problem in future. I have no idea how an extra 0.05mm of lift on the valve opening can make the car run much better - but it could well be that you can convince yourself after hours of sweating and swearing at an engine that it is in fact running better LOL - if they had hard evidence like any extra 10 mpg then maybe it would be worth while. Ever noticed the car seems to run better after it has just been cleaned ? what would you think if after slackening and re-tightening the tappet screws if one of them came loose later and caused a problem ?
I will do preventative maintenance on a car such as putting redex in every so often, spraying plugs and sockets with ACF50 ( especially the ones under car and under wheel arches) and changing brake and clutch fluid every couple of years ( which will prevent corrosion in the system). I have no problem with necessary jobs like oil and filter changes and brakes ( cleaning and greasing slide pins, replacing pads and discs etc.) but to do a job just for the sake of it - no thanks.....
here is a cautionary tale ...
I used to work with a very good mechanic who offered to fix one of his mates cars, there was a problem with the oil pressure sensor ( which just meant the oil pressure gauge did not register properly) - well in getting the sensor out the thread got damaged, he than had to buy a special fine thread tap to repair the thread, while he was using the tap he screwed it in slightly too far and cracked a hole in the back of the engine oil gallery, to get the hole repaired he had to strip the engine down and take the cylinder block to a specialist welder, and then re-assemble the whole engine and re-fit it back into the car - whenever I think of doing un-necessary work on a car that story is the thing that makes me think twice. ££££££'s worth of work for a simple oil sensor worth a couple of ££'s.