well, if carburation is fine (which I think it's not, and running too lean at tickover), then it's a compression issue.
So it's too lean.

Pull out a plug, white?

Too lean meaning I need to turn up the mixture screw? I will check the spark plugs tomorrow...

Unscrew for richer.
sure its idle fuel +/-, not an air bypass. so:
righty tighty=weaker
lefty loosy=richer

And then increase or decrease the tick-over screw to suit?

yep.

put simply:
get engine to operating temperature first!

1. Turn idle up nice and high (1500-2000rpm~)
2. adjust mixture to get highest possible rpm.
3. adjust idle back down as desired
4. if idle wont go low enough- turn mixture screw inwards as little as possible

(the idle jet may be worn, having too big a hole, letting in too much fuel, requiring more air to be at right mixture if this *idle too high even when idle screw at end of travel and mixture correct* is the case - fitting a new idle jet of original bore will cure it)

Will I be able to adjust the two screws with the air filter pan in place or do I need to remove it?

Allways adjust the mixture with the airfilter in place.

So it's possible to do then?

yes, you can easaly acces both the idle and mixture screws with everything in place.

Volodspec, I dont see how this is possible as the T-Nipple (the bit that sits between the underside of the air-filter pan and the top of the valve cover) is in the way of the mixture screw? As I look at my carb (from the passenger side of my car) the small pipe that comes out of that T-Nipple goes around the carb to the left making it impossible to get at the mixture screw? Should this pipe go around the carb to the right as that would then just about enable me to get at the mixture screw?...

I had my car MOT'd this morning and one of the failures was a perished hose that connects to the servo pipe. The mechanic reckoned that that was what has been causing my running problems all this time.

I've replaced the hose along with the plastic T-Nipple which was split but not picked up in the MOT. My car seems to be running a bit better now although I did the solenoid test suggested by "Pettaw" which proved that my idle solenoid isnt clicking and therefore not working...

Update as of today (Thurs-31st-January) I cut the needle/plunger on my idle solenoid and my cars now running fine with no run-over after turning off ignition. It just goes to show that it was the idle solenoid all along. I will replace it though within the next few weeks with another one from a scrappy...

2nd update later today (Thurs-31st-January). I should never have cut off the needle as my car is now running like an absolute pig, my revs are high when accelerating and as soon as I stop accelerating my car cuts out. Off to the scrappy tomorrow...