There is no British diplomatic representation in Comoros. Consular assistance is provided by the British High Commission in Port Louis, Mauritius.
Crime levels are low, but you should take sensible precautions. Avoid any crowds or political gatherings. See Crime and Political situation
Piracy is a significant threat in the Gulf of Aden and Indian Ocean. Sailing vessels are particularly vulnerable. See Sea travel
There is a low threat from terrorism. See terrorism
Take out comprehensive travel and medical insurance before you travel.