When looking through the related paperwork when I purchased my flat, I noticed an indication of the £3000 heating work and television system work on the horizon. Neither the agent or the seller offered up this information, I was lucky to spot it. This was three years ago. I purchased with a £4000 retainer against these invoices and 3 years later they have been issued. It makes it even more difficult when such time passes but for sure the seller would have been aware of this work on the horizon, but whether they had any legal obligation to tell you I do not know. Good luck with it.
On a related issue, has the capping of the current work at £15,000 been confirmed by Camden? I’ve not had anything official and nothing since a speculative estimate of nearer £20,000!