Hi everyone
I have been trying to revive my non starting Stihl HS 45 Hedgecutter and whilst going through the usual checks, Fuel,
Ignition etc a thought occurred that querying through Google has returned various answers. So I wondered if the forum had any views.

Namely I have established by using an in-line spark plug tester that the Ignition Module is generating a spark as evidenced from within the Tester.  However does this mean the spark plug is actually working?

To try and resolve this I unscrewed the spark plug and on grounding it there was a spark detected both within the tester and at the spark plug.

However there was a suggestion (via Google) that the spark plug could be sparking whilst unscrewed but when screwed into the cylinder and under compression, the spark could be suppressed.

Having cleaned the Carburettor, bought a new Ignition Module, disabled the Kill Switch and using new fuel I am running out of
options.

Hi Les, and welcome to TGMF.

The only testers I would use are the ones that actually show you a live spark between two  metal probes at a set distance. 

The ones that go inline and light up or flash I have had mixed results, some say it's got a spark because it flashes when you pull it over, but although the voltage is good enough to light the bulb there's not enough juice to give it a good spark at the plug.

Have you checked the flywheel key? (Note: On the HS-45 the key is cast into the aluminium of the flywheel and not a separate key). They have been known to shear especially if the engine is excessively flooded when you pull the start rope and the engine suddenly hydraulics.  Same applies to some of the cheaper end STIHL chainsaws such as the MS171 - MS181 etc.