I was surprised about the suggestion that there was a change in the type of ownership in 1865 - many y before the 'great reforms' of 1925. Law of property act
but that seems/may be the case
enfranchisement of a lease (seems to be) acquiring the freehold or extending it. Perhaps it comes from becoming a freeholder and therefore under the 1842 act a voter
see:
http://www.landregistry.gov.uk/professional/guides/practice-guide-27
or google enfranchising a lease
The first Act on this is the 1967 act and that involves a tenant doing it (against the will of the leaseholder). Presumably you dont beed an Act if someone is doing it voluntarily.
The usual difference between a leaseholder and a freeholder is that a leaseholder wont do a damn thing, so enfranchising it, would be a first and necessary step towards development.