[Your supplier's address]
[Reference: account number and bill]
I write concerning the above account. The meter is currently showing a reading of [insert reading].
I do not accept that the meter is recording accurately.
The bill in question [reference] for [£...] is significantly higher than it should be [add details of any special circumstances eg, if you were away from the property].
I inspected the meter with all my [electrical/gas] appliances turned off and noted that it continued to register [...] units of [electricity/gas] consumption.
It is clear that either the meter is faulty or that there is some other problem.
Either way, the bill is not a true reflection of [electricity/gas] used. I now wish to request you to carry out a test on the meter at my home.
I look forward to hearing from you with a suitable date for the test to be carried out.