Huge bees? are you sure their not wasps or hornets? Huge bees usually suggest the bumble bee family, they are pretty harmless but will usually nest in rotting vegitation under a shed or similar.
Sounds like you've got a cornucopia (collective noun) of Porcus Guineas Vittigera.
These flying striped guinea pigs are found all along the south coast. Whereabouts do you live?
If it's a swarm of bees you need to contact the council or a local beekeeper, once they are clumping then they will come and fetch them.
Mind you, if they are that big.... are you sure you're not hallucinating?
As far as I know, only Honey Bees actually swarm and they are quite a small bee. Has someone near bye got an attractive plant that's just come into flower attracting bumble bees? A spilled bottle of soft drink would also attract them.
you can get lots of bumblebees together when there is a nest baby bumbles are really cute and not that large... I would guess they are a group of pipistrelle bats who support celtic as their European away shirt is black and yellow stripes