What you have there is a beautiful example of a missing sector orb weaver (Zygiella x-notata most probably). These are harmless spiders & if you look hard enough you will no doubt find them around & occasionally inside just about any house in the country.
Your photo clearly shows the spider's cephalothorax (head) has 2 distinct colours - brown with a dark central stripe, tapering back towards the abdomen. Also a thin, dark line around each side. False widows typically have a more even colouring accross the cephalothorax.
The central marking on the abdomen is more like a feather/flare, with a dark line running down the middle. Again this is not typical of false widows, the noble false widow (S. nobilis) has a marking more like a shield, or pentangle.