Thanks to everone who identified the fact I need a new coil. I would like to buy one of them fancy yellow jobbies, but due to the fact I am skint I was looking at something like this-
http://www.ebay.co.uk/itm/170804677416?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Are they any good or is it a load of old rubbish?

I've no idea if that particular make of coil is any good, but I've no reason to believe it wouldn't be. What that is is a generic after market motorbike coil, which can be used on almost any twin cylinder wasted spark engine, or as one of a pair on a four cylinder.
If you've still got basic points on your engine then I don't see why you couldn't use pretty much any dual output coil, although I await verification on that. If you've got 123 or electronically assisted ignition then you'd need to stick with a coil of similar primary resistance, or risk burning out the electronics.

I still have points (I think) and a Boyer Bransden ignition fitted so I don't want to blow anything. Will this coil damage the black box?

No its the same coil as Boyer sell for their systems

I bought one to test( will post up some intresting results of other tests after i recover from going to the pub to bulk buy Guinness) but never got round to it as i didnt have any screw in caps nor did i like the hard wired vynil leads which i reckon will go hard in weeks like the old red Bougies

also note that they are designed to be bolted to a heat sink - like a motorcycle frame - via that bar so it can shed heat

i can send you one if you want as long as you promise to fit it and let us know how it goes.

What is the profit of using an improved coil?
Where is the advantage?

If you've had a coil overheat, Then you really do appreciate it when it's no longer a worry.

Ι agree.

Anyway last time my overheated coil gave me starting troubles I changed it with the spare from the boot.
Besides that there is no other benefit?

I still carry a spare in the boot, But when a direct swap between the harley style coil i got from ecas, and the original type, the engine starts quicker from cold and hot. It seems to do a better job than the original in general, however, if my old coil didn't conk out all of the time, i would have kept the original - as Sean has said a few times, a pricey coil wont fix poor running issues. (but in my case it did)

all it fixed was a below par coil!

you get a hotter longer spark which helps in marginal situations like cold starting - hot starting and higher revs

when i used the resin coil for the first time the mid to top range was noticeably improved