When calling out an engineer to sort the problem (and sharpen the blades) he suggested it may be the carburetor.
Present day!!
I just completed an oil and spark plug change. The mower started 1st time and ticked over; still out of time and with a little misfire. I again completed a few lengths of the lawn, after which the mower cut out; In fact, the mower was then only happy ticking over.
I have adjusted the mixture to make it richer, which allowed me to complete the lawn. The mower is still a bit nervous when getting going, and does not tick over like a happy engine should. As I said earlier, there is also a little misfire or cough/splutter. Would prefer to keep using this mower as we prefer the quality to the nasty B&Q mower we also have.
Is it the carburetor or a settings issue?