In the end, it wasn’t a bad journey for John McConnell and Hannon. Trainer and horse survived the 10-hour trip by road and wind-whipped ferry from McConnell’s yard in County Meath, Ireland, and were well-rested before Hannon’s start in the 1.30pm at Cheltenham on Friday.

“The journey wasn’t too terrible,” said McConnell. “He’s travelled well, he ate and drank on the way, which is great. He’s had a good chance to rest and he should be fine.”

A growing concern for the likes of McConnell at the Cheltenham Festival is that the challenging process of moving horses between the UK, Ireland and France – the three powerhouses of western Europe’s thoroughbred industry – may become even more testing because of the Brexit crisis.

For decades, a tripartite agreement has allowed the frictionless transportation of horses for racing and breeding. A no-deal Brexit or uncertainty over the departure date puts this at grave risk.

McConnell, a vet as well as a trainer, said there was nothing worse than being stuck in traffic – or a port – with a racehorse becoming distressed and then arriving at a course suffering from a kind of equine jet lag. “The worry is that unless there is a deal there will be problems and delays.

“I feel sorry for Theresa May. I don’t think anyone would come out of the position she was put in smelling of roses. People didn’t really know what they were voting for; how hard it was going to be.”

Cheltenham is generally a respite from everyday worries. Every March, whether the course is bathed in early spring sunshine or battered by rain and wind as it was this week, race fans descend upon Gloucestershire to immerse themselves in the proceedings.

Royals and aristocrats rub shoulders with rock stars, city types, farmers, gamblers and partygoers out to sink as many pints of beer and glasses of champagne as possible.

The tweed outfits, the sharp suits and hats are a sight to behold and there are always memorable stories, such as Bryony Frost making history this week by becoming the first woman to ride a grade-one winner at Cheltenham.

The event is huge for the local economy, bringing in £100m every year. Thousands of temporary workers staff the bars, the restaurants and the gates. The local hotels and pubs enjoy their busiest time of the year. No wonder Cheltenham voted to remain and pro-EU campaigners continue to run a passionate campaign in the Regency town.

But what makes the jump festival so special is the influx of Irish people. Horses, trainers, jockeys, owners and fans from Ireland have come to dominate Cheltenham.

“The whole jump year in Ireland revolves around Cheltenham,” said Denis Egan, chief executive of the Irish Horseracing Regulatory Board. “Every time a horse wins a race in Ireland from September onwards all roads lead to Cheltenham. The main difficulty in planning for the future is that nobody knows what is going to happen. I can’t believe what is happening in Westminster.”

Michael O’Leary, owner of Tiger Roll, talks to the media after his win in the Cross Country Chase during day two of the Cheltenham Festival. Photograph: Tom Jenkins/The Guardian

Michael O’Leary, the CEO of Ryanair, found himself being asked about Brexit as he celebrated in the winner’s enclosure after the success of his horse Tiger Roll. “It’s hard to follow,” he said. “It seems to change day by day. Everybody wants to see a resolution.”

At the Guinness Village, where 265,000 pints are consumed during the festival, a group of Irish twentysomething fans were drinking with a group of English women they had just met. “Cheltenham is one of those times when the Irish and English can get together and have a great time,” said one of the Irish men, Steve Parish. “We’re two little countries,” said Lily Taylor from England. “It’d be a shame if Brexit pushed us further apart.”

Any sudden downturn in the UK’s economy could also impact the tens of thousands employed in racing on both sides of the Irish Sea and the Channel; from farriers to farmers, from jockeys to office staff.

Charles O’Neill travels the world promoting the racing industry as CEO of Irish Thoroughbred Marketing. “It’s Cheltenham this week but I was in Abu Dhabi last week. Then Tuesday I’m in Macau; Wednesday, Hong Kong; Thursday, China,” he said.

His first task when he is in the Middle East or Asia is to explain that Ireland is not part of the UK and will remain part of the EU. “Brexit is the big topic of conversation everywhere,” he said. “What we need is a deal that lets the industry flow and allows everyone to get on with their business. Imagine what it would be like if fewer Irish horses were travelling here.”

A family attend Ladies Day on day two of the Cheltenham Festival. Photograph: Tom Jenkins/The Guardian

Will Lambe, executive director of the British Horseracing Authority, has been planning – on government advice – for a no-deal Brexit since the start of the year. “It’s hard enough to predict what will happen on the track here let alone in Westminster,” he said. “But the main scenario we have been working on is leaving without a deal.”

The UK has promised not to put up barriers to the free movement of racehorses after Brexit – but thus far the EU has not reciprocated. Lambe said his priority was the welfare of the horses and that delays at borders were bound to put extra stresses on them. “We’re hoping that sense will prevail,” he said.

Henry Beeby, the group CEO of thoroughbred auctioneers Goffs, was in the parade ring admiring a horse that his firm had sold twice. The animal was now worth hundreds of thousands of pounds after a Cheltenham win.

He said: “We have a business on both sides of the Irish Sea so we’re in the EU and Britain. Historically, it’s one business – Irish and British bloodstock are indelibly linked. We’ve enjoyed free movement of horses between Britain, Ireland and France for many years. If there’s a no-deal Brexit and that falls away it could make things very difficult.”

If the UK deal does crash out of the EU on 29 March, a big test will come six days later when the Grand National meeting at Aintree in Merseyside takes place. “If Brexit happened with a no deal you could see big problems with getting Irish horses across,” said Beeby. “The politicians have let us down badly.”