The installers should have put the fence up facing away from their property so that their neighbour gets the ‘good’ side. This in practice should be repeated with each neighbour so that everyone receives one ‘good’ and one ‘bad’ side.
As mentioned though, this shouldn’t be taken as a definite. You can’t assume this was done by each neighbour. So, how can you find an official answer to this burning question?
Determine ownership with title deeds
For an official and accurate answer, dig out the title deeds for your house. A copy can be found among the paperwork you received when buying your house, or if lost, ask the solicitor who did your conveyancing. If the information isn’t listed on the plans, you’ll need to check with the Land Registry.
When looking at the plans, ownership is indicated with a “T” which will mark one side of the boundary.
If you can see a “H” (which is actually two Ts joined together) the boundary is shared by both parties: