Wedged garage air hose under tyre so it was nice and slack, it came loose, unnoticed it wound back in to the machine whilst I was filling the rear, gave a violent tug to the tire valve and snap, hiss, BUGGER!
Hoping to get a replacement valve fitted in the morning before heading to Donny.
Ian 
Where are you now Ian? if I can help, let me know, you have my number.
When I read the title, I thought you were going to say you’d snapped a valve stem… snapping a tyre valve suddenly seemed like good news 
Thanks Sean, all sorted in the end, just worked from home and popped to the tyre fitter.
Still, what a nightmare! Of all the things, to be bitten by a recoiling air hose.
NOT AT THE TIME!