The only way to determine the exact cause of cracks is to seek professional advice from a structural engineer / building surveyor before any remedial work is undertaken. Please note failure to detect the underlying cause can lead to repairs not lasting.
All building materials shrink or expand with time. Clay brickwork expands over time and concrete brickwork shrinks as it dries out. The risk of shrinkage cracking is minimised by the introduction of movement joints at no greater than 6 m centres and the avoidance of panels of brickwork where the length: height ratio is greater than 3. The use of brick reinforcement can also reduce cracking. Please refer to ‘Guide to the Use of Tobermore Concrete Bricks’.
We would advise that you seek expert advice from a structural engineer who can determine why this cracking has occurred and can also provide recommendations on how to prevent this on future builds. Through years of experience we know that micro cracks in brickwork is extremely unlikely to be a product related fault.