By not paying the ground rent, you have probably put yourself in breach of the lease, which might well put off any prospective purchaser, especially when their solicitor gets involved. You could presumably pay the ground rent arrears now, to clear that particular aspect. However, I note that you say that "the freeholders haven't done anything". Does this mean that the lease also contains clauses about the freeholders carrying out repairs etc, and you paying maintenance charges, which have also been ignored for the past 15 years? If so, this could present quite an obstacle, especially if any prospective purchaser needs a mortgage from a building society. Finally, the lease may contain a clause requiring you to inform the freeholders of any transfer of the lease, so you may have to contact them about this. My advice would be to read the lease carefully, to identify any potential snags; or, if you don't feel up to that, get some legal advice, before putting the flat on the market.