Four men have been arrested and 19 canisters of nitrous oxide seized after police stopped a car near the Appleby Horse Fair.Officers stopped an Audi RS6 from Leeds just before 11pm on Friday and found the loot alongside more than £1,500 in cash.All four were arrested on suspicion of possession with intent to supply a class C drug - they remain in custody.Cumbria Police said it was running its biggest-ever operation - with more than 200 officers working 24 hours over the weekend - for the horse fair, the largest traditional gypsy and traveller gathering in Europe.Officers also found 'a significant quantity' of balloons in the car which can be filled with nitrous oxide, known by the slang terms 'hippy crack' or 'laughing gas', and inhaled.Detective Superintendent Dan St Quintin, gold police commander for the fair, said: 'This was another successful proactive intervention by police aimed at keeping people at the Fair safe and preventing criminality.'Nitrous oxide poses serious and well-documented risks to health and is illegal to possess or sell for recreational use.'Our officers will continue to act against anyone suspected of being involved in criminality – regardless of which community those involved belong to.' Police found 19 canisters of nitrous oxide, balloons and more than £1,500 of cash in an Audi near the Appleby Horse Fair The horse fair, held annually in the Cumbrian market town, is the largest gathering of gypsy and traveller communities in Europe Horses were seen in the water on Saturday as owners took their animals for the traditional horse-washingIn the early hours of Friday police seized 99 potentially dangerous 'pyramid rings' from a vehicle heading to the horse fair.Officers stopped the vehicle near the Cumbrian market town around 1am on Friday as it travelled towards the fair's trade fields.Police said the rings would be destroyed as they can be used as weapons in fistfights.The seizure came a day after officers found air weapons and counterfeit toys also destined for the trade fields at the annual event.As part of police monitoring efforts officers are using live facial recognition technology to track the faces of those attending the gathering. Travellers enjoyed the sun as the Appleby Horse Fair began in the Cumbrian market townSome 10,000 people were expected for the week-long event, which has prompted Cumbria Police's largest-ever operation Officers used facial recognition technology as the fair began, which compares live images of individuals to a police watchlistCameras will capture real-time images of faces and compare them with a watchlist to find those of interest to police or who are wanted in the courts.Billy Welch, the Gypsy and traveller representative on the fair's organising group, said most of the community did not mind police using the technology 'at all'.'Every major festival, every large gathering like Appleby, if you go through the airport, they've got facial recognition,' the 65-year-old said.'It's just everywhere. It's just a part of life now. And myself, personally, I'm not really bothered about it. The majority of Gypsies and travellers don't mind it at all. And if you've done nothing wrong, well, you've got nothing to worry about.'But others in the community oppose the facial recognition tactics, with reformed ex-prisoner Tommy Joyce, a campaigner to stop 'anti-gypsy discrimination', telling the Daily Mail Mr Welch was similar to an 'informant' for 'allowing' police to use the scheme. Owners parade their horses on the 'flashing lane', where travellers demonstrate the speed and agility of their animals for potential buyers Caravans flooded the streets of the town as travellers prepared to gather and trade horses Water levels were high in the River Eden as the fair began, with event bosses warning attendees not to enter the water themselves Two women rode their horses through the river in high waters on Saturday at the horse fairHe was echoed by John Reilly, founder of the Gypsy Traveller League, who has said 'no travelling man sits with police while members of his own community are being targeted, stopped, searched - and even locked up.'Appleby's horse fair has run for 250 years, only being cancelled twice in that time: first for the foot and mouth outbreak in 2001 and because of the Covid pandemic in 2020.It was once thought the fair originated from a royal charter to the borough of Appleby from King James II of England in 1685, although more recent research has found the charter was cancelled before it was ever enacted.The gathering is sometimes known as 'the New Fair' because Appleby's medieval borough fair, held at Whitsuntide, ceased in 1885.The 'New Fair' began in 1775 for sheep and cattle drovers and horse dealers to sell their stock.By the 1900s it had evolved into a major Gypsy Traveller event which brought families from across the UK and Europe.