Looks like a family business, his mother has also been imprisoned for fraud.
https://www.manchestereveningnews.co.uk/news/greater-manchester-news/mum-of-playboy-drugs-boss-24566455
Shameful, i must of imagined that young dead and naked Israeli girl on the back of a pick up being paraded and spat upon by men? and children, i sometimes have sympathy for the Gazans, and then that image appears.
Is the room below in use? lumps/slabs of concrete are going to fall, slab may continue through to next door, you may weaken the walls below, not an easy job, Alastairs suggestion above would be easier(y)
You could use a solid 65mm engineering brick cut down the middle if you prefer to use bricks, (no need to cut out existing brick) but can't see an issue using a cut down dense block.