When I finished reading He’s the Devil, Tobi Coventry’s “room-mate from hell” debut novel, published last month, I needed a moment to process it. The chilling but often funny horror story that plays out made me reflect on my flatsharing experiences. I’m 53 and live alone (finally) but I had eight flatshares during my 25 years in London. I left the city when I was 49 and bought my own home in St Leonards-on-Sea on the south coast.

So I wasn’t surprised that data from the flatshare site Spareroom revealed that the over-45s now account for 16 per cent of the flatshare market in the UK, up from 10 per cent in 2015, while the proportion of over-65 flatsharers has tripled. And the under-25s? They actually now make up only 26 per cent of the flatshare market, down from almost a third (32 per cent) a decade ago.

Coventry’s book reminded me of some of the red flags I brushed off as quirks, the pressure I’d felt to stay in places even when my wellbeing was under threat, and how much I assumed that other people value cleanliness as much as I do. But it turns out sharing your home with someone you know can be as risky as living with someone you don’t.

My first flatshare was in a dingy flat in the East End of London, already occupied by a friend of a friend who urgently needed a new room-mate after the last one left without much notice. He was a sweet, gentle character I rarely saw, but it quickly transpired he didn’t like to clean — at all — not even after cooking elaborate evening meals such as slow-cooked Moroccan tagines and exotically spiced curries. As someone who likes to live in a tidy, clean environment, I became not just a room-mate but a cleaner.

• The kids won’t move out — so we built them an extension

No flatmate is ever perfect, myself included. One person usually ends up cleaning more and one is generally more considerate. A flatmate I once had gave a house key to her relatively new florist boyfriend (let’s call him Adam) without telling me. Yes, Adam did fill our home with fresh flowers every week but he also redesigned our garden into a flower show-worthy oasis, which was beautiful to spend time in but a completely unnecessary and valuable gift for our difficult landlord. Then came the puppy, a Yorkshire terrier who, before long, was peeing on our lovely hardwood floors and pooping under my bed if the door was left ajar. I’d explicitly and repeatedly said no to a dog, yet it appeared one morning on the understanding it would live with Adam. And then after a falling-out with his own flatmate, Adam and the puppy were set on moving in.

I fortunately escaped that overcrowded set-up just in time to move in with a long-term friend who could no longer afford his one-bedroom rental and wanted to split a two-bed. Citing a busy work schedule, he left me to do all the research, liaise with agents and handle the viewings. He agreed to my choice without seeing the place, and we moved into a beautiful two-bed with a garden, just in time for summer. On paper it was perfect: central London, decent rent and built-in companionship. In reality it took a few weeks for the cracks to show.

• How can I get rid of my disruptive flatmate?

I got used to his habit of regularly cooking for one and eating his evening meal with headphones on. Respectful of his need for alone time, I adapted, but I gradually became aware that I was living with someone who preferred to live almost entirely in their own space. There were tantrums if I invited friends over for dinner, even with a week’s notice. He’d refuse to join us and then ignore me for a day or two afterwards, so I stopped having friends over. He was very protective of his routines: if I interrupted him while he was watching TV, I’d get curt, almost hostile responses, and when my bathroom was out of action after a burst pipe, he suggested I use the shower at my gym. Nice.

His moods became changeable; some days he was fine and others he was distant and irritable, and I found myself feeling increasingly on edge at home. I’m quite house-proud but he was so extremely tidy and ordered that it made the shared spaces feel more like somewhere to pass through very carefully than to actually relax in. After a year I moved out under the pretence that I could no longer afford the rent. He took it badly, calling me selfish, and made the atmosphere in the flat very uncomfortable until I left. He apologised a year or two later, but the friendship never recovered.

During one particular flatshare with a flat-owning friend, she decided to do a full renovation mid-tenancy, and while my room was being remodelled I was relegated — for more than a week — to sleeping on a fold-out in a living room that doubled as a building site. The subsequent months living in the newly designed space largely made those sleepless nights worth it, but before moving into what would be my final London houseshare, I asked tentatively: any planned works?