Property legal advice Uk please

Hi all,

I have recently moved into a detached property and noticed that my neighbour has built a metal sheet over his side of the alleyway, connecting from my house to his despite being a detached property.

I am able to see this from the front of the property and it isn't the prettiest thing and also from the window in the landing.

Whilst this may sound petty, if it serves us no advantage, ie we are able to make use of this, I don’t believe it should be connecting from our property especially if a detached property

He is currently using this to store his ladders and we have no access to this despite it being connecting from our property to his.

My question is, whilst he has built this over his sole access alley way, is he able to do this as the property is detached and the metal sheet is touching our property despite being detached?

Any help is appreciated thread!