Can any one tell me how to open the bonnet as the cable has snapped, tried to access from underneath but impossible,

Is any cable left hanging from the catch or has it snapped off right by the release?
If there's some cable left hanging them try fishing it through the grille with a coat hanger, spray it with WD40 and try opening that way.
If no cable is accessible them you will probably have to cut a hole in the grille and access the catch that way.

Here's a link

http://www.fordownersclub.com/forums/topic/35338-guide-to-fixing-common-focus-bonnet-lock-problem/

The car is a S-MAX and the cable has snapped right by the lock, even if i cut a hole in the gril will have to unbolt lock as it is completely covered, is there any easier way

If you take it to a garage they will probably cut the grille too.
It may be worth ringing a couple for quotes and go from there.

[sub]Thanks for for that guys[/sub]

I think you have to access the back of the latch from underneath - car on ramp - lots of tools & swearing I believe!

What ever you do, don't cut a hole in the grill. This is a really easy and straight forward job. Minimum tools and no swearing! I parked the car up on a kerb so I could get under it, then undid the bolts (10mm and 8mm) that hold the drip tray on. then push the whole tray towards the back of the car and it just pops off. Watch your eyes, it will be full of dirt. Then, lay on your back and look up through the gap. You can clearly see the lock mechanism. Unclip the sensor (a bit fiddly but makes it easier for the next bit). You will be able to see 2 x 10mm bolts either side, you can get to these easily with a small socket wrench and when undone, be careful because the lock cover will fall onto your face. Once the cover is off, you can see the catch lever at the bottom, flick it to the left and hey presto, bonnet open! 

Hope this helps, the comments above almost had me attacking the grill with a hacksaw blade!

Given Stimmos suggestion I strongly advise the use of a pair of goggles, or similar. If you do not have a pair of goggles, perhaps a hemet from a suit of armour, a motorbike, or a welders shield :p

I would imagine the OP has fixed this by now given the age of this thread.

 

The key is then to follow SteveTR's how-to thread on the Smax owners club forum to prevent it from happening again.