Mountfield used Tecumseh and Briggs engines (as well as Honda and Suzuki) over the years - the procedure varies, but essentially you will have to remove the recoil start assembly, which may mean removing the entire engine cowl (not as bad as it sounds!). When it's off, you will be able to see why the starter is not rotating the flywheel to start the engine. More than likely, it's just in need of a squirt of WD40 to free up the starter pawls.
phil_saunders(a)bigfoot.com
Phil Saunders
May 2009