Southwark is run by Labour.

The burial policy is a local Labour policy.

The reason why is it is Labour policy is because 1) they consider poorer members of the community would be particularly disadvantaged if there was no local burial option and 2) there is still a preference for burial in some ethnic communities.

Those two groups are considered to be natural Labour supporters.

There is however no legal obligation on Southwark to provide land for burial.

In other words they are pursuing a policy which they have no obligation to pursue because it favours their core voters not because it benefits all members of the community.