If you go to the following webpage you will find information on honey bee swarms and a map with swarm collectors in your area.
Before you call, please check the BBKA website which will help you differentiate between honey bee swarms and other types of bees/wasps/hornets. Please note that beekeepers can only deal with honey bees and, as we are a charity run by volunteers, we cannot guarantee a response.
Swarms are generally harmless, i.e. they will not sting you, unless they are provoked. Please leave it alone until contacted by a swarm collector. Do not let children or pets interfere with it. Generally, swarms collect in one place for a day or so while they find a suitable new home. Once they have decided where to live, they will leave quickly in a large swarm cloud. This is not dangerous but is best avoided.
If the swarm does not move for several days, the bees may become more aggressive as they run out of food.