Could this be an outsourced service or maybe even diverted to a mobile phone?

Raise the issue with the council by emailing customer.services@dartford.gov.uk or ringing them. Ask them what the alternative is. See if you can ascertain whether it does go through to a mobile or a third party. If it's for emergencies, then there's the question of how many calls it gets. If it is a few, then I cannot see why they cannot divert it and stand to the cost.

If they won't abandon it, then contact your own councillors and see if there is anything they can do. You might be able to convince them that the best course of action is to divert 01322 343434 to the out of hours phone or provide another 01322 number specifically for out of hours which is diverted out of hours.