Professional indemnity is written on a "Claims Made" basis.

In essence the policy only covers claims notified during the period of insurance and is not specifically covering work undertaken during the policy term. For example, if you undertook a survey in 2003, and then in 2005 you were advised by the client of a possible claim, you could not claim against the policy you had in 2003, but would in fact claim against the current policy that was in force when you were first notified of the claim in 2005.

This can be a little confusing to comprehend, but it is crucial that you do fully understand it.