The Prime Minister is throwing his support behind a new law that would make life sentences mandatory for the killers of emergency service workers.

The widow of PC Andrew Harper has been campaigning for the change in law after being left "outraged" at the jail terms given to her husband's killers.

Sky's Lisa Dowd reports.

SUBSCRIBE to our YouTube channel for more videos: http://www.youtube.com/skynews

Follow us on Twitter: https://twitter.com/skynews

Like us on Facebook: https://www.facebook.com/skynews

Follow us on Instagram: https://www.instagram.com/skynews

For more content go to http://news.sky.com and download our apps:

Apple: https://itunes.apple.com/gb/app/sky-news/id316391924?mt=8

Android https://play.google.com/store/apps/details?id=com.bskyb.skynews.android&hl=en_GB

Sky News videos are now available in Spanish here/Los video de Sky News están disponibles en español aquí https://www.youtube.com/channel/skynewsespanol