Is this a DiY job, or do i have to use a gas safe registered fitter? I mean, the gas bit won’t be touched, we can still use it now with matches or a standalone clacker to light it.

I done one in my cooker it was only an AA battery that it needed (was a proper cooker .not a hob)

Assuming you can access it easily to clean up any connections it should be straightforward, might just be grease build up preventing the spark.

Nothing to do with the gas supply really. Although turning the gas and electricity off at the mains, and venting off any remaining gas from the hobs before starting is recommended!