What kind of bees are they Susannah? You should call the pest control to remove/relocate the bee hive. If they are honey bees, a local bee keeper would be happy to do the job.

They normally all die off in the colder weather - only the queen will survive and hibernate. So if you can wait until well into the Autumn they should have gone.

That's only if they are bumblebees or hornets, Steragram. Honeybee colonies remain intact--at reduced levels--over the winter, and can still be dangerous even then. Susannah, I would google images of the three names to make sure which one you are dealing with, and call a beekeeper if they are honeybees.

Contact a bee removal specialist. If there is a hive under the floor it could weigh 50 pounds or more. The big problem is trying to locate exactly where it is but they are the experts. This is not a job for a novice as Tug suggests. One wrong move and they will immediately attack all at once and without the proper protection this could be fatal.
Now reading your previous questions you have said that they are not honeybees but bumblebees. Still, I suggest you have a pest control person look at it.

Ah! I didn't think of looking for a question from 2013! live and learn, I guess. Yep, I would wait until the queens are starting hibernation and the workers and drones have died. that will be safer for you, but it may be hard on the queens unless they are in burrows under the shed. In that case, put the new shed on short pylons, with a ramp at the door, so the queens and workers can still come and go next summer.

In the UK these are usually the tiny bumblebees which nest in all sorts of nooks and crannies. My neighbour has the nest box bit of his bird table full of them. We had a nest under a sheet of tin one year and this year they are in the roof of the bungalow. As Stera says, sadly they all die off, natures way, and the Queen will hibernate elsewhere. Unless you have a really friendly Council you will get charged for any advice/removal, probably lots! See if you can find a bee-keeper in your area and have a word with him, he will probably tell you the same as Stera!

If they are honey bees, a beekeeper would be delighted to take them from you, especially in June as the old saying goes "worth a silver spoon" and it won't cost you anything to get them taken away - obviously if they are accessible.

If they are bumblebees, don't be misled by their docile temperament. They will defend their nest & the queen. Bumblebees can sting repeatedly unlike honeybees which can only sting one time.

Thank you for your replies everybody. I have decided to leave the demolishing until October to be quite sure. My main problem really is that the new shed has already been delivered in flat pack and is leaning against the house wall! It is a plastic shed (I succumbed!) and I'm hoping that it will survive for three months covered with tarpaulin?! I had red tailed bees a few years ago but these are slightly bigger and have got a buff, almost white 'nether region'! They just ignore me as I watch them

Not honey bees then, so by October they should have gone.