Roland Perry wrote:
In message , at 16:49:32 on Wed, 17 Jul
2019, Tweed remarked:

Just for anecdata, my iPhone on Vodafone connects without user intervention
to the Underground WiFi. You don’t need to be a VM customer to use it.

That kind of reciprocal arrangement comes and goes, almost too fast to
keep up. But yes, at the moment some Vodafone plans include the Virgin
Wifi on the tube.

I think you will find all the main networks work with the underground
system. See https://tfl.gov.uk/campaign/station-wifi