The body's Beer Barometer found that total beer sales dropped 8.2%, with pub beer sales down 6.3%.
That means the government's beer tax revenues in January and February were ú17 million lower than the same period last year, despite the 18% tax increase, according to the BBPA.
Off-trade sales have fallen for three consecutive quarters according to the Beer Barometer, and it is the first time since 2005 that first quarter off-trade sales have been lower than in the previous year.
Total beer sales for the year to March fell 7%, with off-trade sales down 4.5% and on-trade sales down 8.9%.
BBPA chief executive David Long said: "These figures provide more telling evidence of the intense pressure in one of Britain's most important sectors. With the Budget last week, government tax policy continues to make the situation worse."