It comes down to chicken density, climate, and time of the year. In Britain your climate is probably an asset, you should not have those hot dry summers that can cook grass and turn it brown by July in some years. Not sure how green your grass will stay in the winter.
I have about 350 square feet in my main run that stays brown year around. I also have about 4200 square feet inside permanent electric netting that provides a lot of green in season. Right now I have 10 chickens but in the summer I may get up to 50, though many of those are chicks growing to butcher size. They don’t eat as much as laying hens.
Right now the grass is not growing and won’t until probably March. When it starts growing I’ll keep the chickens in the main run for a week or so to give the grass a chance to get started. They are really good at picking anything green as it sprouts but once it gets established the green can stay ahead of them. They only like certain plants when they have a choice so some of that stuff they don’t like takes over. I have to mow it three or four times a year to keep the bad stuff from crowding out the good.
Not all of that area stays green. There are some bare spots near the coop and main run where they tend to hang out and dust bathe. It gets some shade there too. But in general they have green stuff until it gets so dry and hot that it cools and quits growing. I occasionally water it to keep the grass growing longer.
I don’t know how big your area is or how many chickens you will have. If that area is truly large relative to the number of chickens it does not have to be a dream. Rotating pastures might work for you, give them time to recover. Grazing frames can help. Some people plant certain seeds, clover is a great addition for forage, but your native grasses will probably work as long as they are grasses they eat. Trial and error may be your friend.
I don’t have a good overall photo but this photo shows what my area looked like this past June. Besides, who can resist a broody and her chicks? I don’t know if I’d already had to mow it or not, but I probably had.