Posted: 19/01/2012 at 20:58
My experience of this plant is that it is not a fast grower but is expected to reach up to 3 metres. Thinking of the height of your plant it may very well be the original. Probably time to ask the experts.Try contacting www.jekkasherbfarm.com for their opinion. This is the business of one Jekka McVicar, the' Queen of Herbs' according to Jamie Oliver. Jekka has run for many years an organic herb business outside Bristol. She has won more Chelsea golds for her herbs than anyone else I can think of.
You could also try the Royal Horticultural Society www.rhs.org.uk but you might have to be a member for individual advice.
There is also the National Herb Society which is situated outside of Banbury in Oxon. Sorry don't have the website details to hand.
If all else fails, try contacting your local Horticultural association, better still join it and make new gardening friends.