The little motor that turns the dead lock mechanism in the boot, just behind the renault badge, has broken. You will need to get a replacement. You have two options.
Either go to renault and buy the whole boot locking assembly for roughly £65 i believe and it might be worth picking up some of the pop fixings that hold the plastic trim to the inside of the boot. That has to come off and those things do break.
Or you can order a third party made motor from ebay
http://www.ebay.co.uk/itm/Renault-C...arts_Vehicles_CarParts_SM&hash=item337c6adfa0. For this you will need to take the boot lock assembly apart yourself, take the gear off the spindle from the old broken motor, solder or weld the gear onto the new spindle, then put the whole thing back together. Whilst this isn't a difficult job you do need to have a degree of engineering skill and common sense. I managed it though so it can't be too hard.
To actually get the boot open in the first place you will have to get to it from the inside. Back seats down, boot cover off (the thing inside that lifts as you open the boot, made of furry cardboard), boot lid black plastic off (one screw and 10+ pop fixings), then look for a vertical metal rod. Once you find the rod, push it down and the boot will open. In the meantime whilst you decide how to fix it you can get the boot open like this.