The Met police have tripled their spending on plastic bullets in a single year, according to figures seen by the Guardian.

The force spent more than £500,000 on the ammunition in 2017 – more than three times the average annual spend for the previous five years.

The figures have emerged amid growing fears about the potential for a no-deal Brexit to result in civil disorder. Last month, the Guardian learned that almost 1,000 police officers from England and Scotland were due to begin training for deployment in Northern Ireland in case of trouble in the event of no deal.

A freedom of information request by the Guardian revealed forces across the country have spent more than £8.2m on stocks over the past seven years, with spending dramatically increasing in the years after the 2011 riots.

The figures are based on the amounts paid to the Home Office for the provision of what are officially known as attenuating energy projectiles (AEPs). While they continue to be used by police in Northern Ireland, they have never been used by forces in Great Britain when confronted with street disorder.

Reacting to the figures, Diane Abbott, the shadow home secretary, said: “It is very concerning that police forces would want to stockpile such weapons.

“The money that public bodies have been forced to spend preparing for the potential outcomes of a no-deal Brexit would be better spent on ending the Tories’ cuts to the police.”

Liberty also questioned the increase in spending and called on the police to rule out the use of plastic bullets, which the human rights group said could only serve to inflame tensions.

“Plastic bullets cause serious injuries and can kill. They have never been used to tackle disorder in mainland UK and indeed, during the London riots the Met police rightly resisted calls for their use,” said Debaleena Dasgupta, a legal officer at Liberty.

“So it is hard to understand how they can justify this sharp rise in spending. They must be clear that such dangerous items will not be used, especially as they could kill citizens, inflame tensions and may lead to more violence.”

The figures show the Met was invoiced last year by the Home Office for £500,183.76 of AEPs supplied in 2017. The figure was £149,978 for the previous year. The total for the force since 2013 is £1.2m.

Sources at the force said the AEPs had been acquired because there were more firearms officers in training, resulting in existing stocks expiring.

Spending has also been steadily increasing each year at Police Scotland, Britain’s second largest police force, which was supplied in 2017 with £275,280 worth of AEPs and has been invoiced for £928,138.99 over the last seven years.

The third biggest spender in recent times was the Civil Nuclear Constabulary, a specialist armed police service charged with protecting civil nuclear sites and safeguarding nuclear material in transit, which was invoiced for a total of £893,638.48 since 2013.

An official report into policing of the August 2011 disturbances in English cities revealed police had wanted to fire plastic bullets at rioters in south London but were unable to do so because specialist units had been deployed elsewhere in the capital. The Met’s response to the riots also revealed the force had increased its capacity since the riots “to make more agile use” of the weapons.

Plastic bullets have been linked to the deaths in Northern Ireland of at least 17 people, eight of whom were children.

According to figures recorded by the Police Service of Northern Ireland (PSNI), they were discharged on two occasions of public disorder during April to the end of September last year. Four rounds were fired at two males who were responsible for throwing petrol bombs and improvised explosive devices at police lines.

The Northern Ireland Human Rights Commission, an independent public body funded by the Northern Ireland Office, said it had raised the issue of the use of AEPs repeatedly with the UK government and at the United Nations.

A spokesperson highlighted recommendations in 2013 by the UN human rights council special rapporteur on peaceful assembly for the PSNI to stop using AEPs and calls in 2016 by the UN committee on the rights of the child for the UK government to end their use on children.