Cracked fireback advice

[Stownsend]

Hi we've recently moved into a house with a open fire. The fireplace back seems to be cracked, I've asked our landlord who assures us it's perfectly fine and still safe to use as it was his house previously and he used it, but I'm just a bit leary to use it with it being cracked. I've put some photos below and just looking for some advice really. Thanks

 

[begreen]

It looks like it's starting to breakdown, but all still intact. It's probably ok for a fire. Have you had a local certified sweep examine this?