Sidi
In Australia, you are only leasing the plot for 75-90 years duration and it's the same for Britain, no one owns the plot forever, what happens to the bones of the deceased after the expiry of the lease, I don't know.
U.K
Why have I only been sold the grave for a set period of time?
Legally, graves cannot be sold for more than 100 years. However, we write to owners every five years offering the opportunity to ‘top-up’ their lease. In this manner, the grave can stay in the family indefinitely, though ownership will never be issued beyond 75 years.
What happens when the lease expires, on a new grave for 50 or 75 years?
When you buy a grave you purchase the rights of burial in that grave for a set period of time. If the lease is not renewed, the burial rights will run out.
What happens when the lease expires on old graves for 100 years?
The grave then becomes the responsibility and property of Doncaster Council.
http://www.doncaster.gov.uk/services/births-marriages-deaths-nationality/frequently-asked-questions