what are the bright orange apex topped posts you see in the country hedgerows

They usually identify gas pipe/mains I believe.

They probably mark the position of a secret gas pipeline.
Here, there is a high pressure aviation fuel line running from a depot in Inverness to the airbases at Kinloss and Lossiemouth. It is top secret (eat this message after you have read it) but the line of the pipeline is marked by similar posts so that it can be identified in case of leaks etc.

Erm...excuse me if I seem to have missed the point, but...if the pipeline is secret...why have they marked it???

JUST what I was thinking!!!!!....but having said that....if no-one else but Bulbaholic and the powers that be know what these posts are...its a sort of secret.......in'it......except it ain't now cos all of us know....ha.ha.....LOL

The pipeline was laid about 20 years ago. They dug a trench about 10 feet deep and 10 feet wide across some 30 miles of countryside and hoped that no one would notice it!
No, it is not really 'secret' but no one is supposed to know about it. The post are to identify the line of the pipe if it should ever need maintainance.

Is it the sort that James Bond whizzes through on a scary contraption?

Actually none of these answers is correct.
They are signposts for aliens to direct them towards the wheat fields where they are going to make their crop circles.

lol. I'd go with Bulbaholic's explanation if I were you Swanky!

I thought aliens couldn't see orange?