i can't remember the OP, but elsewhere on this forum there was a similar thread. On that advice, I ended up buying a heavy duty extension lead with a built in RCD for protection. I'm fine at home and work with dedicated charging units, but this was visiting friends / parents / etc.
In all cases, if you get a reel lead, fully unwind it. If you can get one rated 13A or higher thats what you want. Even the 13A are likely to be lower constant load with 13A peak but I went for a sensible option.
This was the one that was recommended - in the UK can be got at B&Q or screwfix amongst others:
http://www.screwfix.com/p/masterplug-heavy-duty-extension-lead-rcd-1g-240v-15m/98422
hope that helps