Sunderland City Council is urging anyone who comes across used canisters of nitrous oxide to report it to them

They say the expired tear gas -Reuters saw used canisters with an expiry date of 2014 -is making people choke.

It has been particularly popular at summer music festivals, with more than two tonnes of used canisters picked up at Glastonbury last summer.

He added that Mr Ramos had used canisters of smoke grenades while entering the office building and "was prepared today to come in".