A refrigerated lorry containing the bodies of 39 people could have arrived into the UK via several different ferry routes.

The vehicle, which is believed to have travelled from Bulgaria, was found by police at Waterglade Industrial Park in Grays, Essex, early on Wednesday.

Essex Police said 38 adults and one teenager were pronounced dead at the scene.

The lorry is believed to have entered the UK on October 19 at Holyhead in north Wales, one of the main ports for ferries from Ireland, Deputy Chief Constable Pippa Mills said.

According to the MarineTraffic website, which tracks ship movements across the world, there were at least five roll-on, roll-off ferries that docked at Holyhead from Dublin on October 19.

Roll-on, roll-off ferries are designed to carried vehicles, including cars and lorries.

Seamus Leheny, Northern Ireland policy manager for the Freight Transport Association (FTA), told the PA news agency: “There is a direct route to Holyhead from Dublin.

“If the lorry came from Bulgaria, getting into Britain via Holyhead is an unorthodox route.

“People have been saying that security and checks have been increased at places like Dover and Calais, so it might be seen as an easier way to get in by going from Cherbourg or Roscoff, over to Rosslare, then up the road to Dublin.”

Possible route of lorry from Bulgaria to UK(PA Graphics)

Irish Ferries runs services from Cherbourg to Dublin and from Dublin to Holyhead, according to its website.

Meanwhile, Stena Line has a ferry service from Cherbourg to Rosslare in County Wexford in the Republic of Ireland.

Stena Line’s ferry service to Holyhead goes from Dublin, according to its website.

Brittany Ferries also runs a ferry service between Roscoff in north-West France to Cork in south-west Ireland.

There are other roll-on, roll-off ferry services to Dublin, including from Rotterdam in the Netherlands, Zeebrugge in Belgium and Gothenburg in Sweden.

Flowers near the scene in Waterglade Industrial Park in Grays, Essex Flowers near the scene in Waterglade Industrial Park in Grays, Essex (Aaron Chown/PA)

A spokesman for MarineTraffic said the WB Yeats ferry arrived at Holyhead on October 19, having left Cherbourg in France on October 18.

The vessel stopped in Dublin on October 19 at 10.42am, before arriving at Holyhead on the same day at 4.30pm, the spokesman said.

A second vessel, the Epsilon, also arrived at Holyhead on October 19, having set off from Cherbourg on October 13.

MarineTraffic said the Epsilon ferry stopped at Dublin on October 14 and made “several trips” to Holyhead over the following days, including on October 19.

The MarineTraffic spokesman said the Stena Superfast X, the Stena Adventurer and the Ulysses ferries also docked at Holyhead on October 19, having travelled from Dublin.

Meanwhile, there are unconfirmed reports that the lorry was picked up in Belfast.

Police said the lorry driver, a 25-year-old man from Northern Ireland, had been arrested on suspicion of murder.