There are two main regions in UK , one is kumaon (nainital area) other is Garhwal (dehradun area). As I am kumaoni so telling about places here.
Everyone can buy land here and there are many outsiders who have built kothis in small places but they come to reside only in holidays/summer time.
Tourists crowd is mainly in famous places like nainital , mussorie or in chardham route (badri-kedar) or corbett park. other places are free from all this noise.
There are lots of small towns (mukteswar area, kausani area, binsar area)where one can buy a land , build a house aur shanti se apna time pass karo. but now a days there are lots of property dealers (quacks) who cheat unsuspecting outsider clients and sold same land to multiple clients.
Now some other things :
as UK hill stations have cold climate so old persons (especially ladies ) can have arthritis (gathiya ) problem. jodo mein dard hota hai. this thing has to be keep in mind and not build house in a very cold place.
Rainy season is aapda season here due to landslides in hilly regions but only in landslide prone zones. There was a famous incident few years ago in local newspapers , a famous bollywood actress , I forgot her name now, was she Lara dutta or some one else , she gave 5 lakh rupees as initial deposit to some property dealer to find her a plot near nainital/mukteswar area. Unfortunately that year monsoon rains played havoc and kedarnath tragedy happened. also there were many aapda related news aired in TV channels . She panicked and cancelled her deal , even forfeiting her 5 lakh deposit