Result! Leebob, your 'dinner knife' suggestion worked! Thanks mate.
For anyone else trying this the guy in the youtube clip does it with the ignition key and makes it look easy but if you've never done it before then trying to do it this way is actually really fiddly!
It took me about 20 mins of mucking around with the key and getting nowhere and 2 mins of gentle persuasion with a dinner knife and open she popped!
So what about the lock? You still want to be able to lock your glove box with your ignition key right? Just take out the handle surround by undoing the 3 screws that hold it in place on the back of the glove box door. Here's the back of the handle assembly:

The metallic looking bit is the back of the lock, it's held in place by 4 plastic tabs. With a bit of gentle Dremel and cutting wheel action the broken handle has its holding tabs cut and the lock is now ready to be slid out and popped into the new surround:
