No it's not a false widow; from the picture I'd say its a missing sector orb weaver Zygiella x-notata. It's a very common species, and around human habitation you are very likely to see them and their circular webs outside around window frames, sills, porches etc. If you put it outside it'll be fine.
It is commonly mistaken for the false widow, but is nothing to worry about.
Thank you Chris, it appears that there are a number of species being mistaken. 6 months ago most people would have just moved the Spider outside but since the press have picked up on one case it has caused people like me to be overly worried.