all my fault but I've managed to break off the tow bar key in the lock - obviously it's flush with the top of the lock so no chance of "grabbing" it with a mole grip or similar. At least the tow bar isn't bolted to the back of the car! Any good ideas or people to ask??

Replace the whole lock - few posts on here how to do.
Buy a replacement, remove existing, fit new etc  Visitor from fullfatrr.com
* GONE. 2012 RR Sport HSE SDV6 Orkney Grey. Now being piloted by RRSTDV8
* GONE: 2011 4.4 TDV8 Full Fat. Amazing piece of kit.
* Current. 1974 Lightweight 2.25L petrol. Old skool
* GONE. Freelander GS TD4 Manual MY2013. Orkney Grey with privacy, cold and clearview packs, armrests (a must!) and a spoiler.
* GONE. Range Rover Classic '93 200Tdi Factory fit
* 1949 80" in family since 1975

I did the same. Still works fine though. Only problem is there's nothing to prevent anyone pinching the tow bar

Just saw this coincidentally ... might be useful dunno

 2016 L494 SDV6 HSE Dynamic Carpathian Grey