Firstly, it emulates the slow, sombre march of traditional funeral processions and secondly, it prevents other drivers on the road from separating the group.
Cars in a funeral procession drive closely to prevent other vehicles from intercepting. But what should you do if you encounter a hearse on your journey?
You should remain respectful to the procession whilst abiding by The Highway Code.
There are no specific rules in the UK regarding funeral processions but moving to a different lane is considered the easiest way to allow the group to pass respectfully.