Firstly don’t panic! Even if still in flight the bees are not concerned about you they are looking for a new home. Even if they have swarmed onto a bush or other object and they will swarm onto anything they are following their queen and will be docile.
Secondly ensure that what you have seen are in fact Honey bees, the first picture below is a Bumble Bee, most swarm callouts are for Bumbles. They are harmless and the nest will have died off by September so if you can, leave them to it. The second picture is a Honey Bee, there will be perhaps 10,000 plus in a swarm. The “Get Help” button below will take you to the British Beekeepers website where you can put in your postcode and find a beekeeper near to you.
Beekeepers do not charge for swarm removal, well only expenses sometimes such as petrol costs, remember they are doing this as a favour. If someone tries to charge you ask to see their insurance! Please do not call out a pest control firm as you will end up with a bill that may be unnecessary and possibly a lot of dead bees. If the bees are in a place that the beekeeper cannot get to they will let you know if you need pest control and work with them to safely relocate the bees.
Swarming is a natural occurrence for bees and the way they increase their colonies, in much the same way we move to a new home that is what they are doing. They may stay for a few hours, a few days or longer whilst the scouts look for a more permanent home. If you see a swarm contact your local Swarm collector ASAP and give them a chance to survive. If possible try and take a picture to send to the collector so they can advise you.
Lastly, enjoy the spectacle as it is amazing to see.