The Earl and Countess of Strathearn visit Scotland - 4th April 2013 

From the Earl and Countess's own press office statement yesterday: "The Duke and Duchess, known as the Earl and Countess of Strathearn when in Scotland....."

vote yes!!!!!!

The royal family use their Scottish titles when in Scotland, that is quite correct as the dukedom of Cambridge is an English title not a United Kingdom title.

Are they known in Scotland as Earl and Countess of Strathearn? I think that's a mistake. Strathearn is a subsidiary title. Their son (if they have one) will be known by it if he doesn't receive apeerage of his own. Unlike Duke and Duchess of Rothesay (which is an alternate title for the heir to the throne in Scotland) Earl and Countess of Strathearn should imo be treated just like any other subsidiary title.

Both titles are in the peerage of the United Kingdom, since they are new creations. Royals usually get peerages with territorial denominations concerning different parts of the UK however. In the past these were never used as titles they were known as in different parts of the UK, but just as subsidiary titles as owned by many peers. The Duke of York for instance was never called Count of Inverness, not even when in Scotland. Perhaps usages are changing but I think this is a made up usage.