There is no set limit, if you’re negotiating informally.  Typically, the longest lease extension will be to 999 years on the basis that this is a ‘virtual freehold’ interest.  This would be possible only by agreement.  Often where flat owners have purchased the freehold the leases will be extended to 999 years and the ground rent reduced to ‘a peppercorn’.  This is to transfer all of the value out of the freehold and into the hands of the leaseholders who have participated in the freehold purchase.

If the lease is extended under statute, the maximum term of the extension is 90 years on top of the unexpired term.  In other words if your lease is currently 50 years the new lease will be 140 years long.  There is no option under the statute to agree a lesser or greater period of extension.  The statute imposes this ‘one size fits all’ solution.

By negotiation any lease length can be agreed by way of extension eg 99, 125, 150 and 250 years etc.