Bonnet catch release not working

[navanman]

Title says it all. The bonnet catch release isn't working on my Megane hatchback. If you pull the handle in the passenger footwell, you can hear the cable moving under the bonnet but it's not popping up the bonnet so the little pull grip in the front grill can be used to open the bonnet.

Any ideas of the problem or how to get the bonnet open?
I presume the cable has broken under the bonnect at the release? Remove the front bumper and undertray to get at the bonnet release?