OP- you really should just have a friendly phone conversation with the police licensing officer. They are civvies effectively, and very reasonable types in my experience. You shouldn’t have to put up with excessive noise way after permitted hours, particularly in rural area, and i don’t think you are being unreasonable to expect this in any way.
As mentioned, the ‘owner’ and ‘landlord/manager’ can be two very different types. The building can be owned by a major UK property company but the manager could be temporary hopeless idiot.
Contrary to Weeksy’s beliefs pubs are not closing because of people like you objecting to noisy lock ins, they are closing because of lethal combination of tax increases, supermarket competition, declining margins, soaring utilities costs, healthier lifestyles, and vulturous Pubco landlords.
You can always support the pub in future by taking your family for regular Sunday lunch there if you feel gulity…