The research suggests that of these, 9.560 were due to failings by the Crown Prosecution Service or within the court system.
The figures are revealed in a new report, Justice Postponed, written by London Assembly Member Tony Arbour.
Common causes identified by the report include a failure to advise witnesses when to attend court, the CPS not receiving Police evidence and barristers failing to call witnesses who are waiting in court.
The report also highlights how some prosecution barristers arrive in court unfamiliar with cases, resulting in delays and wasted court time while they read key evidence and documents.
London was the worst performing region for cases being delayed, with 16% of cases at Crown Courts and 20% at Magistrates Courts being held up.
Today’s report highlights how poor case management and a failure to manage the needs of witnesses and victims is delaying justice and warns the longterm consequence of such failures could be to discourage people from coming forward to report crime.
Across the UK, delayed and dropped cases are estimated to cost taxpayers £17.4m, money which could be better used in the criminal justice system to reduce offending rates.
Mr Arbour said: “These enormous sums mask the even greater emotional cost to victims and witnesses, who may become so disillusioned with the courts that they will not use the justice system again, and, worse still not even bother to report crime.
“Only by getting the basics right will the CPS reduce the number of dropped and delayed cases and bring villains to justice swiftly.
“Witnesses and victims need to know the exact time, day and place to attend, prosecution barristers should be able to see case papers in advance, not at 9am for a 10am start, and the CPS, police and prosecution barristers should directly communicate before the trial to make sure it is ready.”