Be very, very careful with ground rents; when my brother increased the length of his lease, apart from having to argue about the cost of the lease and their charges for talking to themselves under a different name, they proposed a ground rent which regularly doubled so that in a relatively short space the annual payment would be more than the value of the property! They tried to say it was normal but we got it down to a sensible figure eventually. The thing is, the initial figure looked reasonable so it's easy not to appreciate the effect of regular doubling.