When a property is in a state which is either dangerous or 'seriously detrimental to the amenity of the neighbourhood' an order can be made requiring the repair or restoration of the property. However, from your friend's point of view, there's one big problem. The power to make such an order lies with the local authority.
In practice, legal remedies probably aren't going to help your friend. He needs to seek the support of his local councillor or, if that doesn't work, to get the local press involved.
Chris