If the Brexit negotiations have got off to a tempestuous start after the summer break, blame Yanis Varoufakis.

It appears that top of the summer reading list for some senior British ministers was the former Greek finance minister’s book “Adults in the Room”—his account of the Greek debt crisis in which he played a starring role in the first half of 2015.

Mr. Varoufakis has become an unlikely hero to many in the U.K.: To those on the left, he is feted as a leader of the global antiausterity resistance; to the euroskeptic right, he is championed as the man who came close to delivering their dream of destroying the euro. Now his book is being trawled at the highest levels of the British government for insights into how to handle Brexit.

For many directly involved in the Greek crisis—not least in Greece itself—this lionizing of Mr. Varoufakis is surreal. They regard his portrayal of plucky Greece bought to its knees by an inflexible Brussels bureaucracy, while supposed allies stood aside terrified of alienating their German paymasters as seriously distorted.

In essence, many claim that what actually happened in Greece is this: a populist government was elected on the basis that it could persuade the rest of the eurozone to write off its debts with no strings attached. When the eurozone rejected this “have-your-cake-and-eat-it” proposal, Mr. Varoufakis engaged in six months of brinkmanship, convinced that the EU would ultimately capitulate to prevent wider damage to the eurozone—until Athens itself capitulated, signing up the deal that was on the table all along, having achieved nothing but to damage its own economy.