The report just shows <1M so that's all the information I have.

Sounds like you need a better EICR.

Chances are that it's still several kΩ over tens of metres, probably caused by a small bit of damp sneaking past the seals over the years. If so the resulting leakage current would be in the milliamps range - a tiny waste of power, and no shock hazard provided everything's solidly earthed. You probably need some solid numbers to make a decent argument though - above a certain level (10mA say) there might be an argument that the circuits should have high integrity c.p.c.s to assure safety (which is likely to be there for free in a MICC installation, but the details might need double checking for any possible weak points). On the other hand very low readings might indicate a hidden fault (N-PE faults on circuits without RCDs can go unnoticed for years) or some other insulation issue (e.g. insulation breakdown in the light fittings themselves) which would need attention.

One day we'll get people who don't have a financial interest in the remdials to do EICRs.

    - Andy.

The report just shows <1M so that's all the information I have.

Sounds like you need a better EICR.

Chances are that it's still several kΩ over tens of metres, probably caused by a small bit of damp sneaking past the seals over the years. If so the resulting leakage current would be in the milliamps range - a tiny waste of power, and no shock hazard provided everything's solidly earthed. You probably need some solid numbers to make a decent argument though - above a certain level (10mA say) there might be an argument that the circuits should have high integrity c.p.c.s to assure safety (which is likely to be there for free in a MICC installation, but the details might need double checking for any possible weak points). On the other hand very low readings might indicate a hidden fault (N-PE faults on circuits without RCDs can go unnoticed for years) or some other insulation issue (e.g. insulation breakdown in the light fittings themselves) which would need attention.

One day we'll get people who don't have a financial interest in the remdials to do EICRs.

    - Andy.

its slightly amusing that the younger types who have not had much to do with it consider it remarkable

https://www.electriciansforums.net/threads/super-magic-pyro.111368/

mind you if you want icky insulation results try cotton covered wire or dry  paper insulated (oiled paper is far better and is still quite common in UK street mains.)

(page 8 of this PDF of a paper from 1913 makes a fun read for the interested in the moisture and insulation problems faced by a generation now passed.)

Mike.