I have a trip from Exeter to London, traveling by Megabus. My luggage is quite heavy, around 25kg as I come back to my country so there's a lot of things to pack. Do they charge my luggage because it overweights? Thank you so much!
This Megabus page Luggage states
We don’t mind what your luggage is packed in, and we only ask that it weighs no more than 20kg and is no bigger than a standard ‘large’ suitcase. The maximum size of a single bag is 200cm (width + height + depth).
And this Megabus page Luggage policy states
For guidance this must not exceed 62 inches when adding the total exterior dimensions of the piece (length + width + height) and should not weigh more than 50 pounds.
Note that 25 kg is 55 lbs. Also
Please be advised that passengers wishing to travel with more luggage than specified above will have items refused. No refunds will be issued in respect of travel plans canceled by the customer as a result of their excess luggage being refused.
Also on Conditions of Carriage
You may take up to three bags as long as they do not occupy more space than a single bag of these weight and dimension limits.
You can also take a piece of small hand luggage on board with you. This must either fit on your lap or under the seat in front of you and does not count towards your luggage allowance.
On Glasgow-Lancaster-Preston-Manchester/ Liverpool-Birmingham-London services you may be charged for each piece of excess baggage, subject to space availability.
I didn't find any other reference to charges for excess weight. But it is up to you to do the proper research.