Maintaining ‘presentable’ boundaries to your property
Unless it’s stated in the deeds of the neighbour’s property that there should be a physical barrier or the wall (if it is a brick or stone structure) is listed (as opposed to ‘listing’) there is no law that says you have to place a physical boundary between your property and your neighbour’s, be it fence, wall, vegetation (hedge, tree row, even a floral bed).
How can I confirm that the fence is in effect ‘his fence’?
Check that the fence is, in fact, the responsibility of your neighbour. Simply because the fence posts are on ‘his’ side does not mean it’s his fence.
There is nothing in law to say which way the ‘smooth’ (non-post) side of the fence has to face. If a neighbour chooses to put the non-post side facing in towards his garden, there is nothing to stop him, providing the posts themselves are within the boundaries of his property.
Check your deeds and/or with the Land Registry before you decide what to do.
Related: what to do about a neighbour's overhanging tree branch
Can I repair his tatty fence myself?
Only if your neighbour accepts your offer to do so. If you attempt to repair it yourself without permission then you could be found guilty of trespass.
What if the fence leans into my garden because of weak posts or poor quality fencing?
You can shore up the fence from your side (but do tell your neighbour what you’re doing and why. Be friendly about it. There is no point in provoking a situation could turn nasty.
You could ask your neighbour to strengthen it as the fence is now trespassing on your property. If the fence has collapsed into your garden, you can place the damaged piece(s) in your garden back into his but not at the expense of further damaging it.
If you move the damaged fence, take digital photos of where it was, the condition it was in and where you moved it to in case the situation should turn into a dispute.
Can I build a fence on ‘his’ side of the garden?
Yes, within the boundaries of your property, not exactly on the dividing line between the two. Should you sell your house (or your neighbour sell up, then you may have to explain the discrepancy in space to new buyers.
Can I contact the police as I believe it’s providing a lack of security?
It’s unlikely that they would be seriously interested unless, say, your neighbour has a dog and you fear it might be dangerous.
They may have a Community Safety group who can keep an eye on the situation.
What if I think it reflects poorly on our neighbourhood to the detriment of the value of my property?
That is your look-out. There’s nothing in law that says repairs should be done or upkeep maintained unless the structure is considered to be dangerous.
Related: what to do about noisy neighbours