North of WCO my anti-ice/de-ice goes wrong and I'm in cloud above freezing level - gotta get down. Now.
...
Should Luton accept me?
Should I have to pay > £200 for the diversion?
With the big commercial airfields (and Luton seems big to me) then I guess it depends. Would you make a Pan call? In which case, yes and no, of course. If your problem is not serious enough to decare a state of urgency then it's less obvious. Ideally yes and no again, but if they're busy, your problem isn't that bad and you're going to cause disruption then it isn't so unreasonable to pay for it. What's far worse are the smaller airfields with delusions of grandeur. They don't have the busy excuse.