I'd say it is a False Widow. Not good. When I was a kid growing up in Stoke Newington, my mate Steve and I got a job clearing the garden of a well-heeled Caribbean lady who'd just moved into a house near us. She'd put her packing crates in the garden and gave us a few cans of Heineken to help us get on with the job. The spiders we found in her garden made us call a halt. The size of them was scary...bigger than my adult hand is now in some cases. The woman wouldn't come into the garden when we showed her one.
James and rescued a bubble bee from a spider today. Not strictly right, but, I like bees.
MB