I've been tasked by my other half to try to repair a handrail up the
stairs at my mother-in-laws. The house is early 60s, ex-council, and
some(?) internal walls are breeze block. This includes where the rail is
fixed, and over time, the fixing at the top, secured with standard wall
plugs, has worked loose. It's tightened up OK once, but the holes in the
block the fixings are in are getting crumbly, the holes have opened out,
it's not just a quick twist with a screwdriver.

I could probably bodge some bigger plugs in the holes, but I reckon that
would probably fail again.

What's the best approach? Ideally, I'd like to not have to move the
whole rail. Is there any way to stabilize and pack the holes that's
likely to last decent time and the strain of people using the rail for
support?

Is there a resin product that could do this, or is that being optimistic?

Thanks

Chris