Well the pictures show an install with apparently new cables that are both rough and potentially hazardous.I would not say that the electrical installation is rough per say just a bit on the old side.
The new cables are loose in a cupboard that appears to be used for storage, there are two red tube things already mixed with cables. It would be very easy for those cables to be accidently tugged when something was put in or taken out of the cupboard.
The boiler manufacturers correctly require an RCD to be fitted. There does not appear to be one. A failed element where the live element wire comes in contact with water is un-likely to trip an over current device but the fault will result in electrolysis of the water into a highly explosive mixure of oxgen and hydrogen trapped in the pipe work. If the wire then touches the inside of the heater and sparks it could ignite the gases and explode the boiler and maybe other parts of the pipe work. An RCD will almost certainly trip when current flows from the live element into the water and thus prevent further electroylsis.