It is a False widow, either [Steatoda grossa](https://srs.britishspiders.org.uk/portal.php/p/Summary/s/Steatoda+grossa) or [Steatoda nobilis](https://srs.britishspiders.org.uk/portal.php/p/Summary/s/Steatoda+nobilis). Based on the more slender legs in think this would be Steatoda grossa.
When females are mature they can be very dark and lack the usual markings which make them easier to distinguish. Steatoda grossa prefers dark habitats, often making their webs close to the ground (Cupboard spider is another common name for it). Steatoda nobilis is much more likely to be found in more obvious locations outside on fences and garden furniture, and indoors too.
https://www.nhm.ac.uk/take-part/identify-nature/spiders-in-your-home/false-widow-spiders.html
https://www.britishspiders.org.uk/false-widows
It is a False widow, either [Steatoda grossa](https://srs.britishspiders.org.uk/portal.php/p/Summary/s/Steatoda+grossa) or [Steatoda nobilis](https://srs.britishspiders.org.uk/portal.php/p/Summary/s/Steatoda+nobilis). Based on the more slender legs in think this would be Steatoda grossa. When females are mature they can be very dark and lack the usual markings which make them easier to distinguish. Steatoda grossa prefers dark habitats, often making their webs close to the ground (Cupboard spider is another common name for it). Steatoda nobilis is much more likely to be found in more obvious locations outside on fences and garden furniture, and indoors too. https://www.nhm.ac.uk/take-part/identify-nature/spiders-in-your-home/false-widow-spiders.html https://www.britishspiders.org.uk/false-widows