What a big bee! At almost 3cm long it could be a queen Bombus terrestris (Buff-tailed bee).
It looked confused and dazed at first but revived in the sunshine (yes! the sun shone!) and looked a whole lot livelier after feeding on the Buddleia. Bees and other insects have had a hard time of this summer due to lack of calm, sunny days so let's hope for a late autumn.