[hnlmorg]

Depends on what you class as “old”. Remember that a great many British homes are 50+ years old. You certainly wouldn’t have considered having multiple phones in a house when they were built. So the extra socket was added after it was built.

Adding extension sockets was a very easy job. So easy that many homeowners did it themselves.

So it’s very likely your parents and grandparents bedroom phone wasn’t part of the original wiring.