Who owns the boundary fence, and who has to repair it?

There is no general rule — not the left-hand side, not the side with the posts — and every widely repeated shortcut is a myth. Ownership is determined by the title documents, and frequently by nothing at all.

The myths, stated plainly so they can be discarded:

"You own the left-hand boundary" — no basis whatsoever, and it is repeated constantly.

"You own the side the posts are on" — a convention in some places, not a rule, and not evidence of ownership by itself.

"The T mark side owns it" — this one is closer. On a title plan, a T mark on one side of a boundary line indicates responsibility for that boundary; an H mark (two T marks joined) indicates shared responsibility. Where these appear, they are meaningful.

Where ownership actually comes from:

The title register and plan at the Land Registry, which may contain T marks or a covenant to maintain.

The original transfer deed, which frequently contains more detail than the register and is worth obtaining.

Express covenants requiring a particular owner to maintain a boundary.

Long-standing practice, which carries some evidential weight in the absence of anything else.

The uncomfortable truth: in many cases nobody can establish ownership, and the registry title plan is explicitly a general boundary — it shows approximate position, not the precise legal line.

What follows practically:

There is generally no obligation to have a fence at all, or to repair one, unless a covenant requires it. A collapsed boundary fence can simply stay collapsed, and the neighbour's remedy is to erect their own on their own land.

You may not attach anything to a neighbour's fence without permission, and you may not enter their land to work on it without agreement — the Access to Neighbouring Land Act provides a route where access is genuinely necessary.

Replacing a fence on the line requires agreement; building entirely on your own land does not.

Hedges are different again, and high evergreen hedges are subject to specific legislation.

Boundary disputes are notoriously disproportionate in cost, routinely exceeding the value of the land in question. Agreeing and recording a boundary in writing — or using a boundary agreement or determined boundary application — is enormously cheaper than litigating it.

General information, not legal advice.