RS ANDY,
Pm me your addy and I'll pop one in the post to you, £1 ok ?, it may just not be called a SPST, single pole single throw, the most common ones, just look for the numbers 30, 85, 86, 87,, if it has a extra 87a don't worry can still be used, just look for these numbers on the terminal markings on them should be about £3, but if stuck pm me, I know halfords wilco car shops etc all sell them usually for fitting extra spot lights etc.
tabetha