1 hob isn't igniting?

Hi, I have a Sterling hob and one of the 4 burners won't start on the ignition.

I have cleaned the 'sparky' bit and that hasn't done it. I think there's a rubber seal at the bottom of the 'sparky' bit and I think it might have paritially perished.

Would this cause it to stop igniting?

If this is the case does anyone know the website address of this Sterling brand so I can order a new washer?

Thanks in advance