Football clubs could be forced to pay for policing outside London grounds.
The cost of policing games in one year was £6.6m, the report said
The move would save the Metropolitan Police about £4.5m a year - which could be ploughed back into community patrols and other activities.
Police chiefs in London are calling on the government to allow them to levy the charge - which clubs are currently not obliged to meet.
Instead, London's 13 league clubs only have to pay for officers who patrol inside the ground.
Metropolitan Police chief Sir Ian Blair told a Metropolitan Police Authority (MPA) meeting that patrolling commercial events, such as football matches and other sporting fixtures, should not be at taxpayers' expense.
He said: "We are very clear that we are only interested in charging around commercial and large commercial events.
"Who is paying for the journey from the Emirates Stadium to the Tube station? The answer is the people of London are, whether they are there or not."
The report looked at one year, from 1 October 2005 to 30 September 2006, during which time more than 1,300 commercial events were policed by Met officers.
The report found that the cost of policing such events was £9.2m - the Met recouped only £3.9m.
The cost of policing inside a football ground is paid for by the club - a national policy laid down by the Association of Chief Police Officers (Acpo).
But policing the 345 football games involving the 13 London teams during the 12 month period costs the force £6.6m - though some of this was recouped from the clubs.
"Police sought payment for 257 of these matches, but, because the policy is only to charge for those officers deployed inside the grounds, it only recouped £2.1m. As such, the Metropolitan Police Service (MPS) subsidised football to the tune of £4.5m," the report said.
Other sporting events across London - such as rugby, cricket or tennis - accounted for a fraction of the cost.
'No firm agreement'
An MPA report said: "Charging for the policing of football matches has been the subject of much discussion over the years and, in developing their (existing) policy, the MPA met with representatives from the clubs, the Premiership and the League.
"No firm agreement on payment for policing outside football grounds could be reached and the MPA decided that, without the legal framework, they were not in a position to force payment.
"As such, the current policy states that the MPS will only charge for officers deployed inside grounds."