Smith and Stevens on way out of Downton?

There are rumours that Downton Abbey could lose two of its main characters.

Some reports say Dame Maggie Smith (Countess of Grantham) and Dan Stevens (Matthew Crawley) have not signed contracts which would commit them to filming for a number of years.

They are both currently recording series three, but other cast members are said to have already committed to a fourth and fifth season.