Ethan Brown's stint riding for William Haggas at Newmarket in the UK may have ended before it started, after he was detained at Heathrow Airport.

The 18-year-old was set to have a six-week period riding for Haggas at the famed Newmarket training facility, but he didn't make it out of the airport.

In fact, Victorian Jockeys' Association chief executive Matt Hyland even said they put the teenager in a cell after interviewing him.

"Unfortunately, I had a phone call from Ethan's mother this morning at 4am," Hyland explained.

"Ethan had been at the airport, he arrived midday their time, and he got to immigration and was refused entry.

"I don't think he had the appropriate visas to go in, and was there on a holiday but it appeared he was working from their point of view."

Initial reports suggested Brown was going to be sent home immediately but it is hoped the appropriate visa can still be obtained to enable Brown to take up the dream opportunity.

Hyland added: "He is [feeling flat]. It's the first time Ethan's been out of the country.

"The idea around it is really, really good. Mick Kent organised it through his son.

"Unfortunately it's just gone pear-shaped. Given the circumstances over the weekend [the London terrorist attack], you certainly need to have the appropriate paperwork going in there, that's for sure."

Brown's fellow apprentice Lachie King is also bound off-shore imminently, set to represent Australia in the Longines Prix Future Racing Stars (1600m) race on June 17.

Hyland said King's paperwork was in order.

"Racing Victoria organised his France trip, that's happened the last 3-4 years - there's been apprentices go over there," Hyland said.

"I'm sure that's up to speed."