What a good idea . . . I look forward to seeing if anyone has yet grown it.

I'm curious, too. It's probably a winter crop, where I live, but all data is useful.

This might be helpful, though I agree that anyone with actual experience in the UK is the go to.
http://www.heirloom-organics.com/guide/va/guidetogrowingquinoa.html

Just had a look on Google and found several refs to places growing it commercially in the UK.

I read somewhere that picking and processing is pretty labour intensive though as there are far fewer grains per stalk than other commercially grown grains.
I hope you have more success with it than I did with sweet potatoes...please let us know if its successful.

I too am going to grow it this year after buying the seeds in a bargain bucket at a garden centre not too long ago. Perhaps we could compare notes at the end of the growing season to see how success we both were! Good luck with your quinoa!