Belling Sprak Generator Unit Instalation?

Hi,

I have a Belling GHU567 Gas hob, and recently the ignition of the gas has stopped . Previously you pressed the knob down and the spark clicked until the gas lit, now you press it and nothing happens.
After some research I found a spark generator that should fit http://www.cooker-parts.co.uk/10228/info.php?p=12&pno=1&cat=18295&search=&sought= but I was wondering if anyone knew of a manual that would explain the installation process as the normal manual just details instructions for installing the hob and not taking it apart to look at the internal components!
Also, does anyone know if the above product is the correct component to fix the problem that I have described and if so is there any where I can get it cheaper?

Thanks for your time

Richard