I come from the country where, with a few clear exceptions which are laid out in law (the mile on road signs, the pint when buying draught beer) or entrenched in popular custom (measurements of the human body), the only people still clinging to the Imperial system are elderly fuddy-duddies and reactionary Euro-sceptics.
So that's 95% of the measurements people actually use in their daily lives in Imperial measurements - petrol is the only change that's actually had any impact on the popular conscience. Yes, everyone knows that the imperial measurements have been 'metricised', but if you're going out to the supermarket for milk, you will talk about four-pint and six-pint bottles, not the corresponding metric measurement. Otherwise, the other measurements (i.e., the type used in the lab) were in metric for decades before the legal change.
EDIT: But most importantly of all - we're talking about beer in Britain, which is measured now and was measured then in pints. Even the average lout's Staropramen ordered at Wetherspoon's comes in a pint glass, so why must we consume our British beer events from the 19th century in metric?