Big Bumble Bee (insect) in Sweet Chestnut (queen bombus lapidarius)

The Biggest Bumble Bee I've ever seen! It was around 3cm long! Does anyone know what type of bee this is? It seemed to be making a nest at the bottom of this giant sweet chestnut in Savernake forest, Wiltshire, early august 2015 edit: an expert has told me its a queen 'bombus lapidarius' (red tailed bumble bee)