But it comes too late for one unique site, a few miles outside Lesmahagow.

Birk Knowes, a Site of Special Scientific Interest, has been stripped of its fossils over the decades by unscrupulous collectors, who have wrecked the site using heavy equipment to extract specimens from the rock.

''Unfortunately some people have behaved irresponsibly,'' said Dr Colin McFadyen, who is a geologist with Scottish Natural Heritage who manage the site.

And geologist Dr Suzanne Miller who assessed damage caused by collectors at Birk Knowes was recently quoted on a radio programme as saying there were no fossils left there.

''It's a tiny pocket of some rocks that are over 400 million years old, and everything has gone,'' she said.

Millions of years ago Birk Knowes was covered by an inland sea, and the fossilised remains of its tiny fish are unique.

The site has been known to collectors for years - Dr McFadyen said that the Glasgow Geological Society used to collect there in the 1890s.

It is so important it was one of the first places in the country to be declared a Site of Special Scientific Interest when the recognition system was launched over half a century ago, and now Scottish Natural Heritage manages it.

But despite that, it has been stripped of its fossils at least a decade ago and before the site was fenced off.

The main problem was that the site was so remote that it had been impossible to police, although a voluntary warden now helps.

''Collecting is good if people collect fossils on the surface, but now and again people are behaving irresponsibly, digging up huge amounts for their own benefit,'' said Dr McFadyen.

''They are collecting on an industrial scale for their own benefit, and a tremendous amount of damage is done. People are there for days on end with hammers and crowbars.''

Unscrupulous collectors smashed through fossil-bearing nodules of rock, looking for only perfect specimens of fossil, and discarding others.

And private collectors were not interested in the research which a multi-disciplinary team from a recognised body would carry out, noting the strata in which fossils were found.

''Damage to sites is rare but when it does happen it is bad,'' said Dr McFadyen.

Finds too disappeared into private collections, with no-one knowing even what had gone.

A collection of fossils, apparently built up over 20 years, and which could only have been taken without permission from Lesmahagow, is now in a museum in Germany and Scottish Natural Heritage is unable to take any action to have the fossils returned to Scotland.

''But at least they are in a secure establishment,'' said Dr McFadyen.

He hopes that the new code will drawn a line under such actions, encouraging responsible collectors.

''Science depends on people collecting, and tremendous finds are made by amateurs and we support that,'' he said. ''People learn a lot.

''But what we don't want to see if people selfishly destroying sites irresponsibly.

''We want to draw a line under the bad behaviour in the past, and hopefully this will start a new era of collecting.''

The new code calls for responsible behaviour in the collection and care of fossils in Scotland.

SNH drafted the code with assistance from fossil collectors, landowners, researchers, museums and others with an interest in Scotland's fossil heritage.

The Fossil Code establishes a framework of advice on best practice in collection, identification, conservation and storage of fossil specimens.

It includes guidance on how to collect fossils responsibly without damaging them or the areas where they are found.

SNH Director Susan Davies said: ''Scotland boasts some of the rarest and most scientifically important fossils in the world, from some of the earliest land plants to dinosaur remains.

''Our fossil heritage helps us understand the evolution of life on Earth and the geological development of Scotland, and ties Scotland's geology into the global story.

''The Scottish Fossil Code informs the public about this fossil heritage and promotes the enjoyment and educational benefits of fossil collecting by encouraging the responsible collecting and care of fossil specimens.''