I had a medical fora K3 visa which was all fine. After a period of living in the states on my K3 I had to leave for family reasons and return to the UK prior to adjusting my status. I am now pursuing my CR1 visa and have been told I need another medical. I was told this would not be the case. Does anyone know anything about this or have experience with this?

If you're last medical is more than a year ago, then a new medical is warranted. If less than a year, then you may not need a new medical exam. Good Luck on your CR-1 application.

When does your K3 visa expire?

Medical is valid for 1 year, if it has been more than a year since last medical you will have to do one again.

If you are pursuing the CR-1 be aware you will need to provide vaccination records, the records are transfered to a form either at the CR-1 medical in foreign country, or by a civil surgeon in the USA.