Update. The hot water from the taps is scalding so not concerned about bacteria. However the smell is hard to define but is definately a chemical type smell and taste. It's not chlorine but the only way I can describe it is that sort of pool cleaning sweet chemical smell. Quite strong my daughter says but it does reduce a bit after a few seconds if a large cup is filled. Possibly a gas that is agitated in the water on opening the tap ? It doesn't go completely, far from it, but it does reduce if left alone in the cup. I had a sip and it tastes like it smells. We dont use the electric heating element in the tank just the boiler to heat the water. The smell is there from every hot water tap in the house.
Unfortunately the guy that fitted it installed the cylinder so the anode is basically facing the wall, nine inches away, the anode is around 18 inches in length. So thanks a lot pal. The pipes, five of them, will need to be undone, the tank turned and the anode taken out and the reverse to reinstall it. I know why he did it as the pipe access is easier to install from the front but he could have turned it another 45 degrees and used another few bends. So all the serviceable parts were accessible. But hey ho, that was 16 years ago so I'll have to stump up for whatever is required to sort it out. I'm assuming its the anode of course but somethings contaminating the water. Mind you my current, great, plumber has never had to replace an anode even on an older system because its degraded so who knows. I've also contacted Ariston to see if they have come across it