Martin Underwood wrote:

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.

I've never understood why we don't have a 'serious but not emergency' number
to call in this country, something like 888 would be logical. I believe that
that idea has been discussed and may be implemented in the future, although
I believe that they are going to use something far less easy to remember,
like 112 or something.