Below you'll see images we (at House Martin Heating, Locks heath, Hampshire), have taken of the good and bad ways to repair flue holes. Please click on any image below to enlarge...
Below are 2 images of how not to do this kind of work (terrible finish, bricks not matched at all, this brick work finish sticks out like a sore thumb etc)...
Shown (both top images), are of work we undertook for a customer.
We cut out the half bricks and "tooth" in new bricks. Taking care to
get an exact match on existing brick type where possible. The motor lines match once dried.