This isn’t a species we record often. Which is unfortunate as it is an amazing species and it would be great to observe it some more, that is when it is not sunbathing and doing nothing like the individual below.
The pose you see above, with the front two pairs of legs held together is apparently typical of this species when enjoying the sunshine (*1). This lady was pictured on a large garden planter which was hot to touch, something they clearly don’t mind. The females will carry their eggs sacks around underneath their body and the name Nursery Web comes from their habit of creating a web structure in which they protect their young for several days after hatching.
It’s a fairly large spider, especially the females (12-15mm *1) and not easily confused with anything else.
1* Bee, L & Oxford G & Smith H. (2020) Britain’s Spiders: A field Guide. Second edition. Oxfordshire: Princeton University Press