Buildings Insurance Excess

[frobabili]

Hi
I wonder if anyone can help?
Background: We own the lease of a first floor apartment which is a relitively new (4 years max) conversion - the original building was an old victorian alylum, which was converted into many luxury apartments.
The apartment came with the standard 10 year NHBC warenty, and we pay our maintainence charge which includes the block buildings insurance.
When we purchased the apartment about 2 years ago, we purchased from the guy who purchased it fresh on release from the developer/freeholder. At the time the buildings insurance was beleiveed to be £250.
The Issue: Last week our downstairs neighbour informed us water was again leaking through his ceiling (he told us it had happend on a lesser scale a couple of months ago but stopped & he didnt inform us at that point) into his mezanine dining room, and doing damage to his ceiling, walls, carpet & now is starting to leak through into his lower ground floor kitchen below. Our Kitchen is the room directly above his dining room.
Investigations showed that under our kitchen cupboards only relitively minor water seapage, not to a level to be causing the damage to downstairs & no other obvious leak.
Having called in many tradesmen, including our own plumber, the caretaker, & now the managing agents plumber, its been decided its coming from a pipe within our kitchen somewhere likely either in our plasterboard walls, or under the flooring.
When digging into the issue of liability & Insurance excess, we are told by our managing agent that the freeholder has just procured some new buildings insurance & due to the high number of plumbing related claims they have increased the excess from £250 to £2500.
The Question: Can They do that without due consultation with the leasehodlers (we would have been more happy to increase the maintainence payments if given the option), and do we have any recourse against anyone for the costs of the excess... the likelyhood is the pipework thats leaking is within our apartments boundaries, but we understand the build quality below the surface is poor across the development & feel we should not have to be paying or even considering having to pay such an excessive excess.

Any help/advice much appreciated.

Thanks.