Use the McMaster-Carr part number 13105A75. It is a much nicer lock, doesn't clip on like that chintzy universal one, has a lock nut, keyed alike, waterproof. It comes with a couple of different latches. I use the straight one, cut it way down. Overall I've used 4 of the universal ones, and now 2 of the good ones - there's no comparison.
Locks available from Lowe and Fletcher (UK source)
Thanks to Richard Harding for sending me this information via email. In Richard's own words:
I had to replace the locks on the toolbox, and the McMaster-Carr option isn't easily available in the UK so I thought you might be interested in this option, which might be more common in Europe.