What kind of tradesperson do I need for this problem?

[HelpMebeok]

The wall at either side of my gas fire has cracked like this. It used to have marble over the top so you couldn't see it and I had a gas burner installed about a year ago.
What kind of tradesperson would I need to look at this, a plasterer? A damp specialist? It's been like this for about six months and hasn't spread or got bigger.

Sorry, photo attached

I wonder if it the heat that's cracking it, moreso than damp?
Do gas burners require annual checks, if so the gas engineer might know

I'm thinking the plaster there looks like it has been filled clumsily and the surface of the fill was proud, ie standing out slightly from the wall around it. Then whoever was fitting the marble fireplace, offering the marble up to the wall and finding that bit proud, got a hammer and whacked it, denting it in enough to put the marble flat. At least it's not going to get any worse and it isn't damp.

If it was mine, I'd either get a plasterer who doesn't mind doing a very small job, as it could do with hacking out and replastering. An alternative would be to try to smooth it out yourself, fill any cracks with Polyfilla and sand the repair with a power sander when dry. Polyfilla shrinks as it dries so you might need a couple of applications. But your best bet would be a plasterer for a professional job, or maybe wallpaper...