I have had water leaking through to the downstairs kitchen and have recently discovered a gap between the shower and wall, I was wondering whether mould could have grown inside the wall and that this could of contaminated the water supply I am very worried about this, I have a picture that I have found online that looks similar to this
Because, as you suggested, the leak is likely caused by the gap between the shower and wall (and not a leak in the water supply pipe) it's a practical impossibility that mold in the wall somehow found its way into the supply pipe. So, "No", mold didn't contaminate the water coming from the supply line.
This photo shows an improper installation--thus the gap. To repair: remove faucet (twist off, to the left), remove the nipple (threaded part showing), and replace with a shorter nipple. Shorter by the length of the 'gap.' Once the faucet is reinstalled, caulk around it with clear silicone recommended for wet areas.