Fear not, it's not a false widow - it's a missing sector orb weaver, Zygiella x-notata. It's a harmless, common and widespread species, and around human habitation you are very likely to see them and their circular webs outside in window frame corners, sills, porches etc.
It is commonly mistaken for the false widow, but is nothing to worry about. The scaremongering in the media lately about false widows has heightened anxiety needlessly; the following links may be more helpful to read.
Hope that helps put you at ease.
Oh dear, this harmless little spider is, I'm afraid, rather far from being a "horror".
You have there a missing sector orb weaver (Zygiella species, most likey Z. x-notata). These are very common spiders, especially on the exterior of houses, they like window frames. I should imagine that the vast majority of homes in the UK have these spiders...I have half a dozen on the inside of my front room window, literally countless more outside.
They are however, sometimes misidentified as false widows & in some cases those misidentifications have appeared in the media "false widow witch hunt". Even if you did have a false widow above your back door, as long as you were aware of it, this wouldn't necessarily be a problem. There are no deadly/dangerous spiders native to the UK.
If you look at your specimen, the head is brown at the sides with a clear dark central stripe/"v" shape, tapering towards the abdomen (false widows tend to have a more even colouring on the head). The central marking on the abdomen is like a "flare/feather" (noble false widows are more like a shield/pentangle/monopoly house). The sides of the back of the abdomen have a scalloped effect, around the central marking, false widows aren't typically marked like this - they have a pale band around the lower abdomen, with just 2 or 3 connecting lines, on each side, running to the central marking. Mature noble false widows have reddish brown legs, only sub adult spiders have some striping around the legs - your Zygiella has very clear striping around the legs.
Here is an immature Steatoda nobilis for comparison...
...this individual has lived in the same spot in my front room for more than a year. I do evict males & and any I find in the bedroom/bathroom, but they are much less of a nuisance than the press would have you believe.
Thanks so much Mark!! You have put me as ease. I am sure you are fed up with all the false black widow questions and comments lately but you have made me happy today!! Thanks also for the explanation It was very interesting to read and i will keep it for furure reference.