Brutal

"Brutal" is about drugs and, in particular, the real or presumed involvement of governments in the drug trade.

"Here comes McDrug" -- the invented name "McDrug" appears to stand for large-scale commercialization of drugs, by analogy with the McDonalds fast-food chain: the idea is that commercial interests mean that drugs are now sold cheaply, at massive scale, and everywhere, just like McDonalds hamburgers.

"The English love for China tea ..." -- the first three verses refer to the Opium Wars of the mid-19th century. The British government granted a monopoly on trade with India to a private company, the East India Company, which came to rule large parts of India and fielded large private armies. It also imported tea from India and China to India, and exported opium grown in India (including present-day Bangladesh) to China. When the Qing Emperor of China banned the import and sale of opium in China, threatening the profits of the Company, a British military expedition was sent to invade China and force the Chinese to accept opium imports ("send in the army to deal some smack").

"smack" -- slang for heroin, an opiate drug

"live together in perfect harmony" -- an allusion to the song "Ebony and Ivory" by Stevie Wonder and Paul McCartney, with a cynical twist; instead of 'ebony and ivory' living 'together in perfect harmony', the Mekons are saying that 'drugs and guns and slavery' co-exist happily together.

"Where the poppy grew, the soil is dead" -- the opium poppy impoverishes and damages the soil where it is grown, so parts of Bangladesh may still suffer from erosion and damage caused by intensive opium cultivation.

"Drugs have long been the currency of the Central Intelligence Agency ..." -- it has been claimed that the CIA has used drug sales to finance covert operations; one conspiracy theory asserts that crack cocaine was introduced to the United States by the CIA.

"E.E.C." -- the European Economic Community, a European regional trading organization that was later renamed the European Community, and then merged into the European Union.

"a clown steps over the Berlin Wall" -- US President Ronald Reagan

"burning cross" -- burning crosses were a trademark of the racist Ku Klux Klan in the United States; the reference seems to suggest that Reagan, as a right-wing politician, was sympathetic to the ideals of the Klan.

"Perestroika dependency" -- 'perestroika' ('reconstruction' in Russian) was a policy of reform in the Soviet Union under the administration of Mikhail Gorbachev. Gorbachev's reform policies led to a new openness toward the West, and may have contributed to the later collapse of the Soviet Union. Because Reagan was able to claim credit for this, the song alleges that he had a "perestroika dependency".

"Noiseless rocks ..." -- the imagery in this verse evokes cocaine, including crack cocaine. Crack is sold in chunks known as "rocks"; "snow" is a slang term for cocaine.

"NATO searches for a new enemy" -- with the fall of the Soviet Union, the North Atlantic Treaty Organization (NATO), a military alliance between the United States and European nations, was less necessary. NATO military forces were sometimes reassigned to drug interdiction operations, providing them with a "new enemy".

"the big city" -- possibly London, the home base for the East India Company, with a number of important buildings constructed using money from the Company's profits -- including the profits from the Company-controlled opium trade.

"Fenland" -- a district of Cambridgeshire, England.

"Alderman Roberts" -- almost certainly a reference to Alfred Roberts JP, alderman of Grantham and the father of British prime minister Margaret Thatcher.

"the duffer" -- 'duffer' is English slang for a stupid person, especially an elderly one. From the context, it sounds as if a specific person is intended and this may be a nickname. It's not clear who this is, or why he is "on his way to Alderman Roberts".