My employers, a branch of a large supermarket chain has a long bar over the fire doors that has to be removed every morning and put back at the end of the day. When the bar is in place the fire doors can not be opened. Obviously this is open to human error and I have often seen the bar still on the doors after 5pm. Is this safe or legal? Who can I contact about this. My manager has dismissed my concerns.

It's legal as long as it's managed such that all fastenings are removed when the premises are occupied. If this isn't happening it's an offence and management requires improvement or an alternative option considered

Is this safe or legal? 

This is a serious breach under Article 14 of the Regulatory Reform (Fire Safety) Order 2005. As my predecessor explained, the bar must be removed when the building is occupied. 

Who can I contact about this.

If you're concerned about the management procedures, you can send an email to the fire brigade for the attention of fire safety team. You may want to attached the picture as well - a picture paints a thousand words.