To the best of my knowledge there's nothing in BS 7671 for LV installations.

I suspect that it's one of these things that might be better one way in one set of circumstances and a different way in another - e.g. using a substation Earth might risk exporting nasty voltages during fault conditions - which might carry some risks. So might be better being left to engineering judgement.

   - Andy.

would like to know the safety  implication of not  doing it. 

If the cable is left live and then has a 'bottle'  end (like half of a joint but cable comes in and not out again... ) then  it needs to be on all the maps as live and avoided while digging. However, at the end of a street where there is a sporting chance of extra houses being built later or something it is sometimes the right thing to do.

Just leaving the cable floating leaves it open to accidental re- energisation, so something has to be done at the source end, and this allows it to be re-activated, even if only to inject a  tracing signal  if that is ever required, while cutting it short does not.

Earthing it is normally the best option - a fully insulated cable does not really export the earth, and an old lead covered one just gives the place an extra electrode...

It is pretty much essential to earth dead cores that run alongside live ones for any great part of the route, as capacitive coupling means that a 'floating' wire actually floats up to a voltage that can be dangerous to anyone who later touches it. For the same reason when one half of a pylon is turned off to be climbed, the 'off' side is not just isolated but also earthed.

Mike.

Thanks for your contribution Andy

Thanks for your contribution Andy