Removing a fireplace surround and filling empty/sealed fireplace - are vents needed if no chimney?

conanthex

I live in a block of flats and I want to remove the wooden fireplace surround (not the chimney breast) and fill the empty space where a fireplace would go so the wall is flush. There has never been a fireplace there (just the hole) and the top of the hole is sealed. A mezzanine floor was built onto the top of the block of flats about 10 years ago and all the chimneys were removed to make way for the new floor of flats. Do I need vents when the fireplace space is filled or is this unnecessary since it is already sealed??

grumpy_codger

If there is no chimney above I don't see any point in vents. Also, I think it's simpler to cover the hole with plasterboard than to fill it.