Thanks for the replies but bear with me, if I touch the AC supply in this country the black (blue) will not give me a shock but the red (brown) will, so not really understanding how the transformer part works dos'nt the current go opposite.
Pete
The reason touching the blue in this country does not give you a shock (not always true, by the way dont rely on it) is for the reason I outlined above, that in this country the neutral and the earth are connected together within the building's supply. Therefore then you touch the blue wire there is no voltage difference between you and earth and you do not get a shock.
To expand on neptune's explanation a bit, the mains electricity is ac. alternating current. what this meas is that , for a fraction of a second,the electricity comes out of the brown wire, through the appliance, and completes the circuit by going back through the blue wire.
Then the flow of electricity goes the other way, out of the blue wire, through the appliance, and back down the brown wire.
So can you see that because the flow of the electricity is bidirectional unlike dc which is unidirectional it does not make any difference to the transformer which way around the live and neutral are.
This cycle repeats itself 50 times every second