OK, done it!

It's a SICMA connector. There is a cap on the back that retains a rubber seal. Once that's off and the seal is pulled out, there are two tiny slots either side of the connector pin holes and inside these slots you can just see the green plastic locking tags.

I used a thin pin extractor to unlock the green locking tags and then the green front of the connector comes off forwards.

This then exposes the two locking fingers one on each side of the crimp pin. Lift these up to unlock the pin and it extracts backwards.

Tricky little fu*ker.