Steve wrote in
:

The situation: driving on the M25 and come across debris in the road.
Easy enough for me to avoid it but plenty of potential for an
incident.

Should I have stopped and phoned 999 to report this, or is there a
better number to phone (like the Highways Agency)?

I thought at the the time phoning 999 wasn't called for as there
wasn't an accident. Although in hindsight, there was plenty of
opportunity for one to happen.

TBH, I don't even know if the H.A. have a number to call in cases
like this and I find any advice on their website.

So, 999 or H.A.? Advice please...

I would have phoned 999: you were averting a potential accident. Maybe you
should have stopped at a motorway phone and used that instead to report the
debris. However if the debris had been on a non-motorway road such as a
dual-carriageway you wouldn't have had that option and 999 would have been
the only realistic option. Trying to find out the number of the Highways
Agency on a mobile isn't realistic: I wonder if the directory enquiries
service that you chose would even be able to trace them if you could quote
an address for them? I favour the simplest approach which allows you to do
your duty as a responsible citizen as quickly and as possible so you can
continue your journey.