After a lease drops below 80 years, the cost of a lease extension escalates dramatically .
A short lease can also make a property hard to sell as lenders typically lend only on properties with at least 55 years on the lease. There is no clear agreement ( even amongst lenders ) as to what constitutes a short lease but the consensus is that lenders are increasingly becoming more risk adverse. It is more likely that, over the next few years, lenders will decrease their minimum lease term for lending purposes. Some lenders have recently changes their minimum lease term requirement from 50 to 60 years remaining on the lease.
Most buyers will expect a large discount to take into account the cost of a lease extension.
With the cost of extending the lease rising once it drops below 80 years one would be well advised to extend a lease which has over 80 years remaining or selling the property to avoid the increased cost.