The broadcaster said they collaborated with online journal Community Care to compare the 2010-2011 budgets with this year, and discovered the reduction was worth some $885 million in real terms.
The BBC had contacted 56 mental health trusts across England, but not all provided detailed information.
Data from 34 trusts suggested a cut of 4.9 percent since the current British parliament was elected in 2010.
At the same time, figures provided by 29 trusts showed referrals have increased by 18.5% over the same period, according to the BBC.
Last March, Community Care reported that tens of thousands of English citizens with mental health problems were left without social care support due to budget cuts.
The number of adults who did not receive support dropped by at least 30,000 people, or 21 percent, since 2005, according to the journal.
Mental health trusts are part of England's National Health Service, and is traditionally one of the most crucial issues in the run-up to the May 7 UK general election.
