As gas path states the all flying tailplane was designed for the Miles M52, the information was passed to Bell who were having control problems with the X2, fitting this device solved their problem. When Miles and the Air Ministry asked for data about the tailplane they were told they couldn't have it because it was "top secret".
If you have been following the JSF story at all you will see a similar thing happening, BAe are a major partner in the program, the British military a major customer, and we are supposed to have a "special relationship" with our friends in the USA but we have had to fight tooth and nail to get sufficient information out of "our partners" to be able to carry out any necessary routine and battlefield repairs on the aircraft!
Tonker you are quite right we did spend a lot of time developing aircraft for our domestic companies which had limited appeal to others. We do get a little fed up though with a certain US company crying foul every time Airbus gain some governmental support to develope new and exciting aeroplanes when that certain US companies success was based on the US Government funding the total development costs of the 707 through the C135 aerial tanker contract in the 60's, a long time ago but!
We British do not have financial institutions which support innovation, British industry started to decline massively when accountants started to get into positions of influence on the boards of companies and eventually to run those same companies, most of which are now long gone!
Sorry about the rant I am just a very patriotic grumpy old man!