When I press the start button, it just makes a whining noise. If I turn the ignition switched off get out and and rock the Caterham back and forth in gear. Then then get back in press the starter button with the ignition on, the engine will start normally. I once had a Morris Minor with a bent starter motor shaft. It behaved just like that. I kept a spanner in the glove box to turn it a bit. I'd imagine that other faults in the Bendix drive or the engagement with the flywheel could do the same. So start with visible inspection of the starter motor and the teeth on the flywheel all the way round. ... I'd also check the battery voltage at rest, minimum during cranking when it does start, and at 3,000 rpm. And all of the relevant wires and connections including the earths. Jonathan