Are there indentations in the key, where the pins have cut into it?
That happened to me, the ends of some of the pins in the lock barrel had ground away against the key. This caused them to stick and not spring out, so there was no way to release them.
Hopefully that is not your problem, but if you look at the key and see the problem, that may be what it was.
I first had to have my bike recovered, as it happened in a supermarket car park, then collected by a mechanic was able to remove the lock barrel without breaking the steering lock. They sent the barrel to a locksmith who was the one who found the problem with the pins and was able to fixed it.
It was awkward and a little expensive, though still much cheaper than the cost of replacing the barrel completely. But if you can remove the locking mechanism from the bike yourself, though, it might not be too expensive for a locksmith alone.