meeeee – Is it 13mbar at the gas meter?
The network only guarantees 19mbar at the meter generally, and I don’t have detailed knowledge after that but the meter itself should govern the pressure to 19mbar anyway in case there is a spike in the mains pressure.
If it is lower than that, call the gas emergency line on 0800 111999 reporting loss of pressure, they will send engineer(s) to investigate. Could be a smaller than normal service pipe, could be a leak somewhere that you can’t smell, could be issues with the main in the street, blockages etc. Any of this (should) be sorted by the network FOC!
If pressure at the meter is 19, then it’ll be the outlet pipe work that needs looked at by your Gas Safe engineer. “quite a way from the gas meter” would suggest that is the issue to be honest…. but might be something as simple as having a dual service shared with a neighbour who has had new/larger appliances installed and the pipe now can’t support yours at the same time.
HTH. Depending where in the country you are I might be able to help further if you email me.