Who should I contact to replace the gas governor?
Is it upstream or downstream of the gas meter? It is normally upstream (between the shutoff valve and the gas meter).
Preferably, place the regulator on the intake manifold and the gas shut off valve on the gas supply pipe.

Source: Can a Gas Regulator Be Installed Vertically? - Norgas Controls
A gas service regulator is connected to the end of the service pipe before the gas meter to reduce the gas pressure to supply gas appliances installed in the premises.
(emphasis mine)
Source: Medium Pressure Gas | Gas Meters & Installation | Plus Hazards & Costs
In the UK the supplier (in this case Scottish power) is only responsible for the gas meter itself.
The rest of the connection is either the responsibility of the distributor (if upstream of the meter) or the property owner (if downstream of the meter and including the meter cabinet).
The supplier (who you pay for gas/electricity) is a different entity to the distributor (in the vast majority of cases)
The distributor is location dependent in the UK. So if it is upstream contact one of the following.
Regional gas distribution networks
The regional gas distribution networks are medium to low-pressure pipe
networks connecting the national gas transmission networks to
individual properties in the region. There are five regional gas
distribution networks:
- Scotland, operated by SGN
- North of England, operated by Northern Gas Networks
- London, West Midlands and East of England, operated by Cadent
- South of England, operated by SGN
- Wales and South West England, operated by Wales & West Utilities
Source: British gas distribution networks | AquaSwitch
There is also a number of small independent gas transporters
Disclaimer: I work on behalf of a large UK power company.
Further Reading: