Improvements in or relating to gas meters

A gas meter comprising a meter housing, a gas volume measuring system and a valve, wherein the valve and the system are both contained within the housing, an inlet pipe, via which gas is supplied to the system and the valve, and an outlet pipe via which the gas supplied to the system and the valve is fed to a consumer, a first communication port, operatively associated with the system, via which data signals appertaining to gas supplied to a consumer via the outlet pipe are transmittable, the housing being adapted contiguously to receive a module which is effective to provide predetermined meter functionality, which module comprises a further communication port positioned for communication with the system via the said first communication port.