Group    From 1884 

Founded in 1884. Their website states "The Fabian Society is the UK's only membership-based left of centre think tank" and provides the following:
"The Fabian Society was founded in 1884 as a socialist society committed to gradual rather than revolutionary social reform. The name comes from the Roman general Quintus Fabius, known as Cunctator from his strategy of delaying battle until the right moment. The Society's early members included George Bernard Shaw (later described by Lenin as 'a good man fallen among Fabians'), Sidney and Beatrice Webb, Emmeline Pankhurst and H G Wells, Edith Nesbit and Hubert Bland."