This is one of the Cobweb Weavers in the family Theridiidae. It looks a lot like one of the Enoplognatha species. There are six Enoplognatha species recorded in the UK. E. ovata is the most widespread and common and looks a lot like this specimen. However the very similar looking E. latimana and the more brownish E. thoracica are also fairly widespread in Britain. E. ovata and E. latimana are quite common in gardens and fields where there are lots of flowers.