Dude

I am assuming that this is probably a one off and not typical of scenarios you may be dealing with?

This looks like an installation where it is probable that in the past the electrician or meter reader might have just propped up a ladder from staircase to the meter housing and has relied on the structural condition of the housing to stop both housing and ladder collapsing.

[Reminds me of a fatal accident where someone fell down a stairwell whilst trying to access a roofspace - the housing around the access point gave way when a ladder was propped agasint it]

Looks like there are two meters which suggests that this is supplying two flats.

Whatever is done is going to effectively prevent safe access including emergency escape from the flats above.

So, in the medium term it seems to me that the most likely appropriate solution is to get the electricity network provider to move their incoming supply and the meters (and all the other electrical equipment) to somewhere which is inherently easier to access.

[but in line with the rules in place to deter unauthorised access - so locked housing and/or sufficiently high - but not TOO high to enable safe access by the authorised].

In the short term this could be done with a proprietary lighweight scaffold with PASMA trained people as you suggest - but this would mean blocking off most of the staircase.

Not easily resolved.