Hello I am a lawyer with 20 years experience. I will try to help you with this.
This is a spectacularly complex situation. What is the attitude of the occupiers of the other half of the building what are they doing to get their management company to do their work properly? Is there a Recognised Tenants Association for either part of the development?
There are potential actions against the management company of the other half in negligence if they are failing to do their work properly. If they leave the premises insecure and this leads to drug users using the site (hardly surprising in Whitechapel) and the other problems then you and the others on your side may well have an arguable case for compensation. It would be easier to enforce if there was a contractual relation between you and the management company. Do you know if there is. It would probably either appear in or be referred to in your lease.
What do your neighbours say about all this. What about your management company, their clients will be having their freehold investment damaged as well, what is their attitude?
I think the only way to move things forward for you is to meet with your fellow leaseholders on both sides of the development to see if others agree that action should be taken. In a situation like this you will need to instruct a solicitor face to face perhaps sharing the costs among other concerned occupiers. I think the general position is that occupiers of the other half of the development could be able to take action against their management company or the freeholder himself for failing to fullfill their obligations (I assume they pay a service charge) under the terms of their leases. The occupiers of your side may have an action against them in negligence but it is very complex and you need to band together and instruct a lawyer to meet with your face to face.
Thanks so much for your reply. I'm working right now, but, to answer one of your questions, the occupiers in the other part of the complex have apparently tried to resolve this problem with their Management Company in the past but, after the Management Company failed to satisfactorily resolve the situation, they have now, for some time, been refusing to pay their maintenance charges unless the problems are resolved, which has had a further negative impact on the maintenance of the essential services to the complex (security gates, communal lighting etc). So it's a bit of a vicious circle!
This sounds horrendous. The only option really is for you all to get together. In order to force action you may need to form possibly 2 recognised tenants associations and maybe the other half may need to think about trying to establish a right to manage. These are technical difficult issues that require the use of a solicitor. You need to get some like minded leaseholders together to share the costs and then bring the others along with you.