Trimming back brickwork around new door

I have had a new uPVC door fitted and it was set back from the brickwork to the position of the exesting frame.
As the existing froma was very wide there is not much of the new frame showing and I would like to trim 30mm from each side of the external brickwork.
It is an old terraced property with solid walls and the brick are very soft,
I`ve tried a small test cut and it would not be difficult with a diamond cutting blade. Cutting back would improve accessibility to the lock and allow a uPVC trim to finish off nicely.
Would I need to contact building regulations locally.

Wouldn't bother with BCO - it may open a can of worms unnecessarily. The only problem you may have will be if the lintel above the door isn't long enough.