Britbox is owned by the BBC carrying BBC produced shows from the past and present. Acorn has programs from around the British Commonwealth (England, Australia, New Zealand, Canada, etc.). Both on the Roku. PBS has a few of these shows.
Here is a description of the state of OTA in England from a British contributor to AVS forums:
"Watch Doc Martin, etc… and you will see nice UHF yagis on homes… 500 year old homes and buildings with TV antennas!
Yes - rooftop (or at a minimum attic) installed aerials are just a standard thing here. If you build or buy a house it would be really strange for it not to have a rooftop Freeview aerial. If you live in an apartment building or flat conversion you may get a satellite feed, but this would be in addition to an RF feed from an antenna distribution system for OTA. I’ve never lived in a house or apartment without a reliable OTA RF feed in the main living room.
Cable TV is far less dominant here - probably because by the 60s and 70s OTA was delivering decent pictures to most households which had roof top aerials."