Anyone know whether this is the case and if so why?

Last ime I looked into it 6 years ago for a hemp bale building, hemp was very hard to grow in the UK because of the stupid misunderstanding that hemp is cannabis.
Very tightly controlled under license and all that.
I found one grower in Kent who had spent a long time getting permission from the governement.

The destruction/suppression of the hemp industry is one of the biggest corperate scandals of the 20th century.

If you want hemp Mike there is plenty of it grown in France. I drive past fields of the stuff all the time.

I remember now it wasnt Kent, it was Suffolk. These were the guys I contacted.

http://www.hemcore.co.uk/news.htm
Hemcore, the UK’s only commercial hemp processing company, has completed the commissioning of a new £3.6 million industrial hemp processing facility near Halesworth in Suffolk. When running at full capacity the facility will employ 35 people and enable Hemcore to process 50,000 tonnes of hemp straw a year.

I just put in a small order with Lime Technology (shiv + their binder), they're dispatching it next day. Certainly seem to have stock. Maybe they've cornered the market ;)

[edit: I wrote Hemcore above by mistake]

Some hemp, yesterday :)