Frustrating battle with freeholder over roof

I have a very odd scenario and hope I can be advised regarding my best (and most cost effective) option.

One of my properties is a leasehold flat in London. The house is made up of 2 flats. I own the upstairs flat while the person who owns the freehold also owns the ground floor flat, where he lives. He is the person I have issues with.

The roof of the house is damaged beyond repair. It took a while for the roof to get to the present state. The freeholder never contributed towards any of those repairs. This matter has gone on for years now, while damage continues to be done to my property. Last year I had enough and referred the matter to the County Court and luckily got the Court to order him to pay £2,500 towards changing the roof. He still has not paid the money and I’ve gone back to the Courts for a warrant. This is still on-going.

The major problem meanwhile is that the roof needs to be changed urgently. I therefore decided to go ahead with the work myself and got a roofer to start work 2 weeks ago, who I made initial payment of just over £1,000 to. The freeholder, when he saw roof tiles that were delivered to the property for the job, threatened the roofer and his colleagues and would not allow them carry out the job. He is also threatening to get rid of the tiles. Police are aware of the matter but have only suggested we seek legal advice. Things got so bad that we are actually no longer allowed to contact each other directly (which is a relief). 

My most pressing question now is how do I make sure the roof is changed soonest, as damage continues to be done to my flat? I have considered trying to obtain a court order but worry about the (yet another) cost. Is there something else I should consider? Is there another way of ensuring he allows the roofer the change the roof? I worry that with time my flat could become uninhabitable.

Thank you

Matt