Hi I bought an ex council flat built in 1950. I'm on the first floor of a block of 4 flats and have noticed that there is an approx 15x15 inch hole in the adjoining brick wall???? Can this be a fire hazard? I'm a little worriec

Most likely, yes — a hole of that size in a separating wall is a fire‑risk. You should first confirm whether it was intentional, whether a service or duct has been removed, and whether it connects directly to another flat. You also need to check if any services still pass through it, because unsealed penetrations can seriously compromise compartmentation.

Even if the wall is solid brick, a 15×15‑inch opening can allow smoke to spread, and smoke spread is often more dangerous than flame. For that reason alone, it should be treated as a significant defect.

The wall needs to be properly repaired so that its fire‑resisting and smoke‑tight performance is restored.