Okay, I don't know which of these are on Netflix in the UK, so I'll list some recommendations and you can check whether you have access to them.
Each list is in alphabetical order, but I will note that I recommend
The Wailing above the rest because I think it is the best horror movie ever made. It's my favorite movie, so I'm a bit biased here.
Also, note that some of these have extremely disturbing, graphic, and grim themes, so unless you know you'll be able to sit through such movies, let me know whether you prefer other recommendations.
Supernatural horror:
- Annabelle: Creation
- Anything for Jackson
- The Autopsy of Jane Doe
- The Black Phone
- Dachra (Tunisian horror)
- Dark Water (the original, not the remake)
- Hereditary
- Impetigore (Indonesian horror)
- In the Mouth of Madness
- It Follows
- Ju-On: The Grudge (the original, not the remake)
- Ju-On: The Grudge 2 (also the original, not the remake)
- Kairo/Pulse (the original, not the remake)
- The Medium
- The Queen of Black Magic (Indonesian horror)
- Ringu (the original, not the remake)
- Siccin (Turkish horror)
- The Taking of Deborah Logan
- The Wailing.
"Creature features," zombie/mutant horror, and sci-fi horror:
- 28 Days Later
- 28 Weeks Later
- 30 Days of Night
- Bone Tomahawk
- Brightburn
- Cloverfield
- The Descent
- Dog Soldiers
- I Am Legend
- The Midnight Meat Train
- The Mist
- Quarantine (the remake of Rec; both are excellent movies)
- A Quiet Place
- A Quiet Place II
- Rec (I think it's better than the remake, although I like both)
- The Road
- The Thing
- Train to Busan.
Psychological and thriller horror:
- 10 Cloverfield Lane
- Audition
- Bedevilled
- Caveat
- Get Out
- I Saw the Devil
- Us
- Watcher.
Slasher horror:
- Candyman (the original, not the remake)
- Carrie (the original, not the remake)
- The Collection (the sequel to the Collector)
- The Collector
- Halloween (the original)
- Inside (a 2007 French movie)
- The Strangers
- X.
These should suffice for now. Have fun!