> I couldn't find one.

A parliamentary publication from 2018 estimated the uplift factor to be 93x outside London and 287x inside [1]. Found via ChatGPT.

I would think that the north-south variation has flattened a little bit by now, but I can't immediately find any similar document from the last couple of years.

[1] https://assets.publishing.service.gov.uk/government/uploads/..., page 12.

[2] https://www.progressive-policy.net/publications/gathering-th...