I will guess its the gas valve sticking, does the gas line have a dirt
leg to keep debris out. Try tapping the valve next time it wont light.
You say you hear spark are you sure it lights a pilot and not just the
burner. Maybe a weak ignitor

Hey Ransley,
no it doesnt have dirt leg - but thats something
i didnt think of, so i'll give that a go.

As far as the spark - i dont just hear it, i see it, and its quite
strong, so i dont believe its that. But it looks fairly easy to
replace, so will try that just incase.

And you are correct, it does light the burner directly - sorry for the
confusion.