What happens
Found it flat in Islington? Leave it where it is.
Flat tyres in Islington are found at the kerb: a Highbury resident going to the car before work, a Finsbury Park driver back from the station, a Farringdon office worker at the end of the day in a pay-by-phone bay. The car is already in a bay you queued for, and driving it flat to a garage across the A1 wrecks the sidewall and loses the space. The right move is to leave it and call.
Say where the car is and send a picture of the tyre. In the bay the fitter inflates it to trace the leak: a screw in the tread means a repair from inside, a leaking valve gets swapped, a corroded rim seal gets cleaned, and a tyre that went down through a sidewall failure is replaced with one in your size. Choice and cost are put to you before the work starts, in the bay, not in a workshop.
On run-flat tyres? They behave differently once deflated, so check the handbook's limits and read our page on run-flat tyres; we fit replacement run-flat tyres at the car in Islington as well.
Related help from the same Brent Cross team covers broken tyre replacement in Islington and emergency tyre replacement in Islington.