Really? Depending on how old it is, the V40 should have either a Victa 'own label' 2-stroke engine (made of cast iron), or a Briggs & Stratton 4 Stroke engine (made of light alloy).
If it really does have a B&S 2-stroke, it's been re-engined. B&S 2-strokes are rare, and were never fitted to Victa mowers as far as I know.
Regardless, it sounds like the thread has pulled out of the head when you removed the plug. I've never seen this happen on an iron head, but on the alloy ones, it can happen if the plug is over-tightened. In any case, it's technically possible to repair it using a 'helicoil' insert, but a new cylinder head is the preferred repair. Cheap if it's a side valve (or a 2-stroke), not so cheap for an OHV engine.
phil_saunders(a)bigfoot.com
Phil Saunders
October 2012