It looks to me like the VO has been wired in incorrectly. Please take another photo which shows were the cables from the meter go - do they go into the VO at the bottom?
Your PV ac arrives along the black cable into the small enclosure with the gray switch. There should be two cables from this enclosure which join with the two cables from the meter and then go into the VO input. The VO output then goes to the Consumer Unit.
In your current arrangement the solar is connected to the output of the VO when it should be connected at the input of the VO together with the mains from the meter.
The VO should be wired in as shown in Figure 2 on page 8 of 16 of:
https://www.waxmanenergy.co.uk/media/upload/eav00401_pdf02.pdf
You will need to call back an electrician who can rewire as in Figure 2. This is not job for DIY!