Can anyone explain why the Spark should have a different transmission range to, say, the Mavic? They're both drones. They both can do as much harm as one another, so why do we get such a measly restriction on the Spark!?

The spark uses WFi and the transmitting power is dictated by the regulators under the terms of the agreed standards. Mavic uses a proprietary wireless standard that would have been negotiated under the standard agreed by the regulators. So nothing to do with the drone and everything to do with EU regulators. Also WiFi is a spectrum that has to share with every smartphone, laptop & router so it's cluttered. Using 5.4ghz will be less cluttered and the Spark uses the high channels not used by routers, down side is that at high frequencies you lose range. Out of the towns try 2.4ghz you should get a much better range with out all the clutter and a lower frequency.

Thanks for that - it all makes sense. I think my confusion lies in the fact that Spark in the US can fly 2km, so theoretically the wifi can get it as far as the Mavic's restriction. I wonder what the UK regulators have against a wifi controlled drone vs Mavic's proprietary wireless.  Good tip on the 2.4ghz!