No you can't, it complicates the matter considerably if there is a claim, and you have no insurable interest in the fabric of the other five flats. The sellers should be able to tell you who the leaseholder is - this will come up anyway in the searches which your solicitor makes before you put in an offer. Could you not contact one of the other five leaseholders? - they are likely to know, they will have to be paying their ground rent and portion of management charges to someone, even if it's a management agency rather than direct to the leaseholder - and that should give you a lead. When I bought a leasehold flat, the sale documents gave full details of the owner, amount of ground rent payable p.a., proportion for buildings insurance and maintenance of common areas - etc.