The bill for policing the loyalist Twaddell Avenue protest camp will be more than £21m, the PSNI has forecast.

Attempts to resolve the north Belfast parading dispute and dismantle the camp failed last month when a proposed deal between protesters and republicans collapsed.

Loyalists set up the "permanent" base in 2013 after Orangemen were banned by the Parades Commission from marching past the Ardoyne on their way home from that year's Twelfth of July celebrations.

Almost three years on and the policing costs are estimated to now be in excess of £21m.

PSNI Chief Constable George Hamilton told the Northern Ireland Policing Board a cost update would be provided later this month, but added: "It is reasonable to expect the estimated total costs will be in excess of £21m.

"The PSNI has a responsibility to police the Parades Commission's determinations and also to ensure that the resources deployed take account of the prevailing threat at the time of the deployment."

Mr Hamilton also said it should be noted that month-on-month, the costs have been "on a downward trajectory". At its peak, the cost of the Twaddell Avenue policing operation stood at £1m a month.

Talks were recently held between republicans and loyalists in a bid to reach a deal ahead of this marching season. The deal would have meant the Orange parade prevented from returning to Ligoniel in 2013 would have been completed its journey last Friday morning.

As part of the agreement, there would have been no application for a return parade on the Twelfth, and the protest camp at Twaddell Avenue would have been dismantled.

The small site consists of just a caravan, a portacabin and some toilets, but sporadic violence means there has been a police presence there since it was set up.

Last year, more than 20 police officers and a 13 year-old girl were injured when trouble erupted on the return leg of a Twelfth of July parade.

One officer had to undergo surgery to reattach his ear after it was "effectively severed" after being hit by masonry.

However, Mr Hamilton maintained he hoped the fact that a number of parades had already passed without significant incident this year was a positive indication for the remainder of the season.

"In planning for parades we engage and work actively with all relevant parties to try and ensure that events adhere to any Parades Commission determinations, occur within the law and pass off peacefully with the minimum amount of inconvenience to others," he said.

"We operate, as far as possible, with a no surprise approach and base the extent of our resource deployments on each set of circumstances faced, informed by information and intelligence.