Igniter plugs were the bane of our life in the W10. All crewmen generally carried a spare, together with a 2B pencil. If the plug failed you took it out, went round the guts of it once with the pencil and re-fitted it. It would usually give you one start. If it didn't, you had the spare plug (which may or not have worked for you...)
In FEAF for a while there were no spare plugs, so it was 2B pencils only. On one operation, where a speedy departure was called for from an RV with anxious troops on board, the plug failed and so did the pencil treatment... The crewman grabbed an empty milk bottle from the cabin and filled it with fuel from the water drain tap under the aircraft. Then he soaked a bit of rag and lit it, and while the Boss went through the start sequence the crewman poured the remaining kerosene into the sucking compressor and lit it with the flaming rag as the HP cock was opened. The flame front went through the engine and it lit! Bless the Gnome.
When the Squadron was back in UK I got so fed up with raising defect reports on the plugs to no effect that I called the MD of the firm in Putney that made them, for A Discussion. He had no idea there was a problem, all he knew was that the RAF bought lots of them! I told him the milk bottle story above and it was, I think, the only time I have ever heard someone go pale on the phone. Things got better after that, presumably because they started to pay more attention to the quality and integrity of the plug core. The aircraft industry is brilliant if you communicate with it.
Happy days!