Strange Fake Widow Spider Or Fat Fraud?

Spotted this strange fat spider today hanging off my cat! Not sure what species it is but it does have those odd white spots that the fake / false widows have. I know there are quite a few different fake widows in the UK, I have seen a few, but they are usually much darker in colour. From different angles this one was very shiny, almost silver in colour. Is this another one to add to the collection? I believe people and animals have to be careful around these spiders as one woman had to have her finger amputated due to a false widow bite.

Identified as a Theridion blackwalli by the good folks of the British Spider Identification Facebook Group

There have been numerous others that have also had some very nasty wounds from these types of spiders. Is it a fake widow or something else. It's only small, but so fat it looks like it's about to explode! Strange little thing. I put it on a Basil plant and tried to take a few pictures but the camera was having a tough time focusing. Click the pictures to enlarge.