Are joist hangers essential ?

I obviously need to talk to my local building inspector on Monday but wonder if anyone can help me out here - I have a 1930's solid concrete block house, and have started to lift a few floorboards to see what is underneath - seems the timber joists (100x75)just sit on the concrete sleeper walls at either end with no sort of fixing used. There are 2 more sleeper walls across the 3.5m span of the joists.
I am hoping to fit insulation between the joists but am wondering if I need to be looking at fitting joist hangers or is it going to be ok just to leave them as they are - after 80-odd years the floor is level, has minimal bounce and no signs of damp or anything else so would hope I can just leave it as is but I fear the inspector may disagree - anyone got any knowledge that may put my mind at rest ?

If there is nothing wrong with them, then you can leave them as they are

As above they are fine as they are

That's a massive relief - thanks !

I am struggling to get my head around what can be done and what needs to be approved by the BI.
I want to improve my house, will do my best to keep to any regulations but am concerned that at times some rules seem to go against what I see as common sense - many years back I renovated a Victorian mid-terrace house for my mum, and was told by the very young BI that I had to dig out the (dry and compacted) sub-floor, lay hardcore and a concrete slab - this meant going below the footings by over 12". Despite me arguing that it didn't seem necessary and was likely to be risky for the rest of the house it had to be done. I never understood the reasons for this.....

What you need to do will depend on what you are applying for. If your application was for insulating the floor, then the inspector is only there to check the insulation