The bonnet release mechanism on my Cooper has jammed and I cannot open it. Has anyone any ideas for releasing the catch? This is fairly urgent since I need an MOT

 

Has the front end ever been tweaked?
I don't know about a mini. But I had a VW Scirrocco once that woulodn't releas. I took the release handle off and grabbed the cable with a pair of vice grips and pulled hard. It worked until I could get a new cable.
The mini has two cables, one for each side, so yiou may have to pull two cables by hand