Renault managed to solve mine, luckily under warranty, not quite sure what they did with it, i'm not the most mechanically minded! :-S But they had to order in some new parts, and have it in for the day to install. + The hour and a half of me staring at the 265 trophy in the showroom while they scratched their heads!
Initially they tested the signal actually being sent to open the boot, which it was apparently, just that for some reason the boot was not picking up the command. Also did a general reset on the battery to see if the 'turn it off and on again' option would work.
They also had both of my key cards, probably to re-program them after they had fiddled with whatever they needed to.
Also a related problem i found was my rear wiper failed to operate, it just so happened to rain on the way so i told them about that too! I also had the service light on stating 'electrical fault' on the HUD.
I'm pretty sure he mentioned nothing about the mechanism, cold or any water damage with my particular problem however... must be the gremlins again!