UPDATE: So I disconnected the solenoid so I could get a proper look at it (I got my son to film me so I could put it back together) and make sure I ordered the right one. After I'd done that, I put it all back in and connected it up and thought I'd just give it a go.... Started First Time!!! Haha, I wondered if it was just a loose connection somewhere?

I'll order a new one anyway, but just finished mowing the front paddock and kept the wife happy!

Cheers,
Rich