Building extension near drain

An extension built by a previous owner of our house thirty years ago received planning permission. The extension is within 1 metre of a public drain which runs under our property. In recent years, neighbours have had planning refused for extensions within 8 meters of the drain.
Any idea why extensions were allowed close to drains in the past but not more recently? Was the law changed, or did they just 'tighten up' the rules?

Doesn't the nature and depth of the drain have a bearing on how close you can build to it? Of course maybe building regulations have also changed in the intervening years. You can see the current regulations below if that's of any use. Maybe older versions are also accessible online?

It's a storm water drain. About 1.5m diameter. From what I can see now, it looks like the rule is that one cannot build within 3 metres of the edge of the drain.

johnmurch said:

It's a storm water drain. About 1.5m diameter.

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That is some drain, I've been in smaller mines.

SparkRite said:

That is some drain, I've been in smaller mines.

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Where? In Lilliput or something?

ClubMan said:

Where? In Lilliput or something?

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Seriously though, years ago surveying power requirements down in the likes of Arigna.

The miners often had to work in way smaller shafts than 1.5m lying on their backs all day.
A diameter of ~ 5Ft would have been luxury to them.