To ask another dummy question about title plans/boundaries?

Where is the property?Scotland? England? Australia?

If its in England you would need to get either the conveyance deed or transfer. Boundaries with T marks are most likely on the conveyance, however there is no guarantee.

I always thought that, looking out from inside the house, the boundary on the left hand side is yours, was a rough guide to working it out.

I agree @Pinkfreesias
If you stand and look at the front of your property from the road side, you are responsible for any boundary to the left of that. It should be marked on your house deeds with a T.
However, you can pay for and replace any boundary (discuss with your neighbour first) as long as you stay in the boundary lines or bring to your side of the boundary.

OMG OP the usual duff legal MN legal advice, please ignore.

Speak to the solicitor who acted for you the you bought the house. They will give you a copy of the title deed and plan. Simple.

Is it not in the text somewhere in your deeds? Ours are shared responsibility, there's nothing marked on the plans.

It might be on the deeds i.e. any old conveyances or transfers (not the title register or plan) but there is no guarantee that it will be unfortunately.

Nope.
We have shared boundaries on all four sides of our property and annoyingly, responsible for ALL of them

The left hand side thing is total guff, i'm afraid.

PP may have lived in a house where that was correct, but in general terms it's total guff.

Sorry to be rude but PP need to be careful about the advice they give people.

I can't believe people are still peddling that left side/right side guff.

Just wait a few minutes OP, and someone will be along to tell you if you look out at the back/wrong side of the fence then it's yours.

How do you tell which is yours then

When you start the purchase process your solicitor requests a copy of the title deeds and plans form the Land Registry. Hopefully, you'll receive a plan with small T marks which indicate your fences/walls. If not, they may well be described in writing in the deeds. And failing that, there may be some other old documentation. Sometimes though, especially with older properties it just isn't possible to work out, so it comes down to whomever is keen for their to be repairs or maintenance, is willing to pay and so on. Hopefully amicably but often not so.