Have you actually asked him to turn it down at a reasonable hour? And, if so, how has he responded? Until you've spoken to him, and he's failed to keep it down, there's not really much you can do. Sometimes it's best to have the conversation after the event, when no-one's had a drink and tempers have cooled.
When you have spoken to him, and if things fail to improve, report to Environmental Health at the council. They have a statutory duty to deal with noise nuisance. Ours will at least send a warning letter (there are 3, the final one threatens prosecution).
Before you do that though, it's worth keeping a "noise diary", including dates, times, nature of noise and it's impact on you as a family, eg kids awake most of the night, too tired to go to school, etc. The noise nuisance team here won't take any action until they have a list of incidents, so you can pre-empt that by gathering it now. And include when you asked him to keep it quieter/finish earlier, and how he responded.
My council seems to have a threshold where they're much more likely to do something if the noise goes on past 3 am, more than once a month, and if it's on week nights. And they're very good about dealing with noise from barking dogs, because that tends to be daily, so there's no debate to be had about how often it's reasonable to have a party.
Speaking to the agents might do some good, especially if his landlord is the type to be bothered by impact on neighbours, but many don't give a toss what their tenants do as long as they pay the rent and don't trash the place.
The police here won't do anything at all about noise, they'll only turn out if things get violent. We couldn't get the police to come out when a group of drunken teens were shouting and screaming in the street and vandalising cars at 1 am. Even when one of them lobbed a can of beer at my neighbour, cutting his head, they only came and took a statement 2 or 3 days later and of course, no-one knew which of them had done it.
I hope things improve, OP.