From 1 October 2015 British visitors need a visa to enter Malawi. Details of the application process can be found on the Department of Immigration website and the website of the Malawian High Commission in London.
Most visits to Malawi are trouble-free, but you should take sensible precautions to protect yourself from muggers and bag-snatchers. Most thefts from visitors take place around the main bus stations in Lilongwe and Blantyre, and at the main ports for the Ilala ferry. See Safety and security
There is a low threat from terrorism. See Terrorism
Take out comprehensive travel and medical insurance before you travel.