Hey dude sorry this has happened to you - a real ball ache.
Same thing happened to me !
I used a ceramic drill to drill out as much of the spark plug as I need to allow an easy out to grip the metal thread.
Soaked with penetrating spray overnight and a few other occasions.
Then I used an easy-out. it worked but was lucky, non of the garages wanted to touch it without taking the head off and drilling it out.
Tip 1) Pre drill it, otherwise you will struggle to get it to bite however only drill what you need - don't want swarf in the cylinder
Tip 2) Go slowly when using the easy out - they blunt real quick and you only get a couple of shots.
Worst case scenario ... you dont drill enough and you snap the easy out as you turn it too fast !
But it is possible to get out .. heres mine using a halford easy out [second to largest size from memory]
Thanks man. Only last week I started riding regularly to work and really enjoyed the commute. Met a few bikers on the road as well and was starting to get ready for riding through winter! So yeah, massive ball-ache it is.
I appreciate your suggestions on this and am encouraged by your success.
I have ordered a set of easy out extractors from screwfix as well as 2 cans of penetrating oil. I have a car to use so will soak the hole in oil from tuesday evening every day till I get to work on the bike on Saturday.
Also waiting for the long hex bit Paul has recommended to get the pilot hole drilled.
I really want to get it sorted as this bike has some sentimental value and it's just bloody good fun riding it!