I am in the process of attempting to buy a house in the UK; as it has stood for about a hundred years, the deeds feature some unusual clauses. For example, this conveyance from 1921:
(Subject to any necessary consent of the local authority) The right at any time or times prior to the expiration of a period commencing on the 22nd day of December 1920 and terminating on the 20th anniversary of the death of the last survivor of the issue now living of Her late Majesty Queen Victoria to make connection with all or any of the part of the hereinbefore mentioned storm water drains and sewers which shall be so constructed and laid on the Vendor's land by the Secretary of State and to make use of the said storm water drains and sewers for the passage and running of water and soil from the said King's Weston Estate or any part or parts thereof or any building erected or to be erectd on any part of the said Estate PROVIDED NEVERTHELESS that all such connections shall be made and maintained by and at the expense of the Vendor his heirs or assigns and to the reasonable satisfaction of the Secretary of State his successors or assigns and that the Vendor his heirs or assigns shall henceforth pay and bear a fair proportion of the cost of maintaining those parts of the said storm water drains and sewers and their accessories which shall carry the water and soil discharged thereinto by the Vendor his heirs or assigns and that if the capacity of the said storm water drains and sewers shall be insufficient to allow of the reception of the water and soil aforesaid or if consequent upon such reception the capacity of the said storm water drains and sewers shall at any time become insufficient to meet the drainage requirements for the time being of the Secretary of State his successors or assigns then in either of such cases the Vendor his heirs or assigns shall pay the cost of any necessary enlargements of the said storm water drains and sewers which the Secretary of State his successor or assigns shall think fit to make.
Apologies for the apparent lack of formatting - that is genuinely how it appears, punctuation apparently being a luxury at the time it was drafted. What I'm curious about is the use of the life (+20 years) of 'the issue' (her own children?) of Queen Victoria being used to establish a time limit on this clause.
Another condition, added in 1973, (which I'll spare you the similar wall-of-text for) starts similarly:
If at any time during the lives of the descendants now living of His late Majesty King George V and the life of the last survivor of them and twenty-one years after the death of such last survivor (such period being hereinafter referred to as “the perpetuity period”)...
I assume it was not permitted to specify a 'perpetuity period' that was unbounded. But how did unknowable time spans (rather than, say, 99 year terms) come to be favoured for legal documents of this type? Would it always be expressed in relation (ha!) to a monarch, alive or dead? How far up/down the family tree could one reasonably go? Is this still used today (and thus my ignorance is of legal rather that historical matters), and if not, what changed?