Old unused access to a part of our garden is being blocked by locals

Dobeylove

We recently bought a property which had in the past an access to a part of the garden which cannot be reached any other way due to it being 2 metres higher than the other part of the garden and there are listed walls stopping access to the higher level. Approximately 20 years ago, when the access was in use a barn was built on that part of the garden. 
To have accessed that part of the garden you would have needed to leave the highway and pass over about 6 meters of unregistered land. We have aerial photographs showing the access in use.
The problem we have is that the barn is becoming dilapidated and is an eyesore and also a health and safety issue. The garden is in AONB.
I believe due to the access not being used continuously the access is now extinquished? 

Some locals are now blocking up the area with bamboo they have cut down from the unregistered side of our boundary which has also ruined the privacy of our garden, from the area of old access on the unregistered side of the land, even concreting in a bench where we could access from. The police have no interest in the problem as it is considered a civil dispute
There are also TPO's on all of the trees in the garden and we will need access at some point to maintain those too. Added to this is that there is a sewer pipe running underneath the garden that services 7 properties. If there were to be a problem we would obviously need quick access to the garden.
My question is would it be possible to open up the access again and what would we do about the concreted bench removal?

Thanks all 

ThisIsWeird

A lot more info required, Dobey.

For starters:

1) Is this garden yours?

2) Does anyone else have any entitlement to access it - any RoWs, for example?

3) How do these walls prevent access from the main part of your garden? This inaccessible area is 2m higher than the rest of your garden, so where does this wall run, and just how high is it?

4) What is behind the actions of these 'locals'? What do they reckon they have entitlement to?

5) This 'access' to 'your' otherwise inaccessible part of 'your' garden - when was it last used? 

6) When you viewed the property, did you notice this raised part and old barn? Did you enquire about it? 

7) Is this old barn shown on your deeds? 

8) Your conveyancing solicitor would have asked you to confirm that the boundaries shown in the deeds map correlate closely to that observed on the ground, yes? Did you do this - did you walk around the plot, following the boundary, and ponder this raised area?

9) Is there 'anything else' of relevance you are not telling us?

gwynlas

If this part of the garden is simply on a higher level with a retaining wall would it be accessible by ladder? Concrete benches are usually supplied and/or erected by local council can you check with parks and leisure department? If the land is unregistered  and accessible then anyone can use it including yourself to gain access to your land. Given you are in a conservation area you could check with the local officer if this includes the barn and whether you can repair or demolish this.