If you and your flatmate cannot have a normal conversation without raising your voice because of noise outside your flat, you have a serious noise problem.
Your council’s environmental health department deal with noise complaints so give them a ring. Go to Gov.uk to find your local council.
If you share a house or flat and one of your flatmates is noisy, try talking about it with them first. The best option is to find a compromise, for example, loud music is fine, but only at weekends. If the noise is really excessive and you cannot agree a compromise, you could get your landlord involved as well. If you are in halls of residence approach your university accommodation office or the building manager about it.
When complaining to your landlord, bear in mind that if you have a joint tenancy, or the tenancy is in the other person’s name, your landlord may decide to end the tenancy for everyone – not just the person causing problems.