Following the desk survey on the 8th December, today I collected some field survey data. I timed my walk from Holborn ticket hall to my office, walking at my normal pace via the route I assumed best. I timed the walk using the stopwatch function on my smartphone.
Holborn station ticket hall to my office building: 13 minutes
Holborn station ticket hall to my actual desk: 13 minutes 45 seconds
So this supports the Google Maps calculation of 13 minutes, even though I took a different route
Previously I had discounted the walk between my office doors to my actual desk which takes the best part of a minute via the stairs.