G'day nick I'm a new be here to. actually this is my first post. mate I'd pop the plug out. use some vice grips to hold the plug to the mower and re connect the plug lead. check you have the fuel off and give it a tug to check if you have spark. if you have pop the plug back in and get some carby cleaner and clean the carby, you could have had old fuel in there and it gels up.
let us know how you get on.
ta.
sam ks.
