If you have a swarm of bees in your garden?
First be sure of your identification.
wasps - brighter yellow & hairless
bumblebees - fatter and very hairy, usually larger than honeybees/wasps
honeybees - short hairs, colour darker than a wasp (yellow/brown/grey/black)
use the pictures below:
the wasp picture also features a honeybee (below the yellow wasp)

Photo: British Beekeepers Association
Bumblebees. These are the fat hairy bees that visit your flowers for nectar and pollen, or nest in your compost heap ur under the shed. The nest has only a hundred bees and lookd like a pile of brown sheep droppings made of wax and surrounded by a fibrous ball of fluff that was an old mouse nest. Nests in compost heaps or in the ground are usually bumble bees, but occasionally are wasps. Bumblebees very rarely sting unless actually squashed eg by sitting on one that is gathering nectar from clover in the lawn. When annoyed their first response is to buzz extra loud and vibrate their whole body. Stinging is a last resort for bumble bees. Wasps are the worst for stinging, honeybees may sting close to their nest but bumble bees are the least likely to sting. Bumblebees are extremely valuable to the environment for their work pollinating many flowering plants and trees. Always consider leaving the nest alone where it will die in the autumn. Queen bumblebees leleave the nest and hibernate through the winter months to start a brand new nest in the spring.
Guide to British bumblebees
www.nhm.ac.uk/research-curation/projects/bombus/bumblebeeid.html
Bumblebees of the world
www.nhm.ac.uk/research-curation/projects/bombus
Moving the nest is usually fatal to the colony. The stress leaves them vulnerable to destruction by an invasion of wax moths. If you are still really worried then you could block off that part of the garden where the nest is.
Solitary bees. Not so fat as bumblebees, but just as hairy. They look a bit like honeybees, but more hairy and usually grey in colour. Each bee makes its own tiny nest and rears its own young. They eat nectar and pollen from flowers. They sometimes occur in numbers because the soil conditions are good (sandy) for nesting. They are largely harmless, unless you actually sit on one.
Wasps and Hornets. Bright yellow and no hairs. Usually noticed in the late summer on ripe fruit or nesting in the attic, disused shed, or any dry cavity. All you see are wasps flying to and from a hole in the tiles, gutters or air-brick. Wasps sometimes use holes in the ground. Wasps perform a very usefull function in the garden by eating many garden pests. They are carnivores, eating any insect they can catch. Without wasps we would be swamped by aphids and caterpillars. Wasp nests die in the first frosts in autumn. Queen wasps leave the nest and hibernate through the winter months to start a brand new nest in the spring, most die in the attempt, only a few manage to make a new colony next year.
Consider leaving them alone till autumn when the nest will die naturally. They present the greater risk of stings, but can be killed with wasp powder. Make sure you follow the instructions on the packet. Or you can ask a Pest Controler to destroy the nest for you. Try www.discreetenvironmental.com (Andy Martin 0208 391 1101, he is a beekeeper) Your local council usually has a list or try a search for "Pest & Vermin Control" in www.checkatrade.com.
Honeybees. About the same size as a wasp, but hairy and not bright yellow. Colours vary from black/brown/grey, often striped with more, or less, dull yellow. Hairs are shorter than for a bumblebee and commonly has bald patches on some of the stripes. Honeybees visit most garden flowers for nectar and pollen. Some plants like cotoneaster, wisteria, or lime trees can be really buzzing with bees when they are in flower. From April to September some honeybee colonies may swarm. This is when a whole cloud of bees come over and settle in a tree, hedge, fence, etc for a few days before going off to a new home. They fill up with honey before leaving their nest. This is their food for a day or two, and they tend to be more docile than usual while their honey stomachs are full. Honeybees may sometimes make a nest in any dry hole in a loft space, chimney, wall or tree. They can be defensive close to the colony entrance.
A swarm of honeybees hanging on a tree:

photo: David Reygate
If you think it is a honeybee swarm or nest a beekeeper should be called.
Some of our Surrey Beekeepers Association local Divisions operate a swarm collection service. Details on their own websites see links on the left.
Your local police station or council often has a list of local beekeepers. Don't use the 999 service, There is a number for your local police station in the phone book.