Checked resistance on HT leads and it seems they were slightly corroded and needed a bit of a clean up with some wire wool. After plugging them back in to the coil they seemed to be ok. Resistance was good and had to push them in while srewing in tightly.
Might be a good tip to anyone who has a problem with cylinders not firing rather than go out and buy £50 worth of coil and HT leads! Luckily, I tried this and it saved me a few quid