Pretty sure it is not, certainly not acceptable for a gas appliance which is all I dealt with.
Apart from any other reasons two come to mind, blockage of the vent by ash and any wind blowing in through the vent will push fumes and hot embers out of the hearth into the room.
I find it odd if not allowed given that some stoves have an air supply tube behind direct to outside .
Ive seen other intallations with air brick behind ,infact the property ive moved into has the same thing which i thought was a good idea as the fire got air from close by instead of dragging cold air accros the floor.
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