Thanks for looking but I'm afraid, what you thought was a timing mark was actually only a speck of dirt from my garage floor. :-(
And also, I appreciate that age was not made clear and I didn't mean to sound grumpy by saying why did you need to know.
I also realized today that that the crank case gasket is broken so I've searched the internet but only been able to find a gasket set! Anybody know where I can get just the single gasket? (apart from American websites, as I'd have to import them!). Going back to the timing, I think I'll just have to go with trial and error using the top dead center trick as I cannot see any timing marks.
Thanks to you all