To see if your meter is a Half Hourly one you will need to go to the Meter and look for the supply number sticker that looks like the one shown below. If there is a double zero ’00′ next to the S then your meter is definitely a half hourly one;

It is also worth noting that if the number in the box next to the S reads ‘05’, ‘06’, ‘07’ or ‘08’ then it is possible that you could also have a half hourly meter
http://www.allaboutsavings.co.uk/business-electricity/half-hourly-meters/