Is it possible to get international health insurance for a visit to the UK once you are already in the country? A friend who is staying with me on a visit from America did not get medical insurance before coming over, but would like to get it just incase. Can you just apply online and set the trip start date to anything after today, or is this considered fraud? She has relatives in the USA who can mail over any documentation that is sent to her home address.

Thanks in advance!