[DanBC]

I was going to say the BT Museum, but that closed to visitors in 1997(!).

The replacement is "Connected Earth": https://en.wikipedia.org/wiki/Connected_Earth

> Connected Earth is a UK network of organisations, primarily museums, that preserve the history of telecommunications in the UK. Heritage artefacts are physically dispersed to Connected Earth partners and other institutions as appropriate, and are brought together again online through virtual galleries, searchable catalogues and educational resources at its website.