Do it yourself as been available for some time now, but they do send a meter reader occasionally, to see if you are 'up to date'. Alternatively they will provide an estimated reading, but I have found that this is usually 'in excess' of what you might have used. But they will correct the bill and send a fresh one, if you phone up.
I know when we had a bit of a query once about meter reading, I was a bit alarmed that 3 different contact companies were involved. No wonder the bills can be high!.