If I knew someone who had a place in the London Marathon but has injured themselves in training and now doesn’t think he can run it, what’s to stop me taking their number and running in their place as they are not interested in deferred entry for next year?

You may need to get them to sign on for you – not sure if they need photo ID now.

Other than that, nothing.

Actually you can authorise someone to collect your number on your behalf…so providing you’re the same sex as the runner then there isn’t a problem. Obviously if you were found out you’d be banned from future entries etc but this is more of a protection at the elite end of the field.Another consideration is the next of kin notifications in the event of something nasty happening>