We've done some UK long distance walks but the easy way with booked B&B accommodations and luggage transfer. We did encounter other walkers using rougher overnight accommodations from tents, to camping barns and hostels.
https://www.yha.org.uk/camping-and-cabins/camping-barns
Like the idea of camping but want to shelter under something more
substantial than fabric? Try a night in a camping barn. These "stone
tents" offer simple accommodation with a communal area to prepare your
meals, relax and sleep.
Our camping barns have running water, showers and toilets and cooking
facilities. You won't need your sleeping bag, as we provide all
bedding and make the beds. You might want to bring warm clothes, a
torch and walking boots.
https://independenthostels.co.uk/england-bunkhouses-campingbarns-bunkbarns-hostels/
England : Accommodation in bunkhouses, hostels, camping barns and
bunkbarns
Staying in English independent hostels, bunkhouses and camping barns
is a great way to tour England on a budget. Self-catering
accommodation with stays as short as one night enables couples,
individual travellers and families to experience landscapes as varied
as the North Norfolk Coast, the Lake District and Cornwall right up to
Northumberland. The cities are also well provided for with boutique
hostels and backpackers providing great value city centre
accommodation. English bunkhouses and hostels also provide ideal
accommodation for groups, particularity those looking for outdoor
activity breaks, with sole use of large kitchens and dining rooms.
There are nearly 200 privately run English hostels in the Independent
Hostels UK network, providing accommodation in England’s classic
countryside, National Parks and historic towns and cities.
And in Scotland the term for hut/ huts is bothy/bothies being a primitive shelter with a roof.
https://www.nationaltrust.org.uk/holidays/bothies-and-bunkhouses
What is a bothy?
Bothies offer stripped back accommodation in remote locations. Close
to walking trails and national parks, they’re a great option for
walkers and people who want to get away from it all. Simple brick or
stone structures, bothies offer a 'camping with walls' experience.
There's usually no electricity and water often comes from handpumps