Water main stop valve

[Tinminer]

I'm in north Devon and served by Southwest Water. I have a remote water meter location (over 800m away) and have been trying to isolate a potential leak - problem is there is no conventional stop valve in the meter chamber. There is an inline fitting (see photo) but I don't know what its function is. There is a slotted
screw on the top but this is seized. Any suggestions..?

 

[CountryFan]

Hard to tell, but just after the meter is there a small white connection that receives a hex key or does the water run the opposite way, eg meter then what appears to be a pressure reducing valve?

 

[Tinminer]

Pressure reducing valve makes sense. I've had another look and there no visible means of turning off the water - the meter connects directly to the pipe either side. I'm hoping South West Water can advise further...

 

[Madrab]

Seems a bit of a stupid install from the supplier if there's no way to shut down the mains to service the meter or PRV. Possibly find that there's a toby further upstream on the communication pipe but, as suggested, that'll be for the transporter to advise.