Essential Rubber in Hackney, if it isn’t too far for you. 27 Downham Road, N1 5AA. Telephone - 0207 241 0055 or Burwins on Essex Road also N1, 0207 359 3050
I work near Gillette Corner - had a puncture the other week and called my recovery company - they sent Revolution Motorcycles who fixed it in about 2mins… Obviously will charge if not covered by recovery, but they are quite close to Brentford - Norwood Green - so you may be able to ride there rather than pay a call-out???