Hi vernonk. I am certainly no representative of a southern water company and in fact I have written several letters of complaint to MPs and cabinet ministers (under the last government and this) complaining about the charges for unmetered water services as the basis of those charges seemed extremely arbitrary - ours seemed to be double that of larger families we knew were going up by double the rate of inflation every year for no apparent reason. I was arguing for stronger regulation as there is little if any competition. But no-one in government seemed to want to change anything other than recommend a meter.
in the end I decided the only way to achieve a fair price in our case was to go for a meter. And it worked because our bills fell dramatically. As a result we are also much more careful to avoid wasting water (2 minute showers not 10 minutes ones, turn hosepipe off while shampooing the car, use collected rainwater to water the flowers, etc).
So to me a meter is great, but the savings were maybe higher than some people will get because our unmetered charges were particularly excessive.
However, getting back to your original question, it's essential you get your meter checked. Good luck