Ian, re keysafes don't get a "Master" one; there was one fitted at our new spot in Buxton, which took me a minute of so to open once I'd seen the relevant Youtube video.
The one I fitted at my Dad's seemed secure, and was insurance company approved, but I can't find it at the moment to check the make.
The only way to get it out of the wall, would have been to remove the bricks, as I used a couple of rawl anchors.
You used to be able to get mechanical number keypad locks, with a key override, such that they can be used with a conventional key as well; not sure if they are still available.
At my Dad's I used to keep copies of front and rear doors keys, as he was prone to either leaving the key in from the inside, or dropping the night latch.
Fortunately I got to know the very competent carers, and showed where I'd hidden the special screwdriver.
I'd put a sawcut across the end of the inner back door mortice lock key on my Dad's copy, and they knew how to engage the driver into the key from the outside. (it was only the kitchen door he left the key in, rather than the outer rear porch door, so the property remained secure.)
Living in Sheffield, I think I'd drop into Harrold's on Shalesmoor, and see what they have to offer, as I'm sure there will be newer products available now. https://www.hharrold.co.uk/
None of this helped when a paramedic locked the back door, and pulled the front one so hard that the front door closed even with the night latch dropped.
When he was released from hospital and dropped off outside by the taxi driver, he was then locked out and wandering around most confused; fortunately a neighbour found him and broke in.
Bill