Key in. Turn. Lights up. Check neutral. Depress starter button - half turnover but no firing. Release button slowly - engine turns and fires.

Wtf??!

WD40 the switch, dodgy starter relay/connections and/or dying battery ( but there should be other symptoms with this)

Thanks mate. Checked battery terminal connections and they are okay. WD'd the switch aNd generally had a poke around. No improvement. It starts but I worry it won't. It's still doing it. Very odd.