Woodburner blanking plate broken

Our home woodburner had been letting out a bit more smoke into the room than usual, and probably dangerous fumes as well. When I looked round the back of the stove I discovered this. The stove is on the left, can you see the crack?

From inside, after removing the baffle, you can see that a piece has fallen off the blanking plate which covers the unused flue exit.

From the front nothing looks amiss. This is a Cottager 01 stove, which we had fitted 18 years ago.

The blanking plate is normally hidden by the baffle - or throat plate - which itself was a bit cracked and distorted but I don't think that matters so much.

We are having someone to come and sort it out next month. This would have to be the coldest time of the year.

This is our view of the sun breaking through the fog this morning.