The Ministry of Defence initially thought the munitions dump in the Irish Sea that has dogged plans for a transport link between Northern Ireland and Scotland was 10 times smaller than it really is.
Defence officials also believed that dumping had only started after the Second World War - when it began after the First.
Proposed by Boris Johnson in 2018 at an estimated cost of around £20bn, plans for a 21-mile bridge connecting Northern Ireland and Scotland were widely criticised at the time.
More recently, rail industry leaders mooted building a tunnel from Larne to Stranraer, with a price tag of around £10bn.
Doubts have been cast of the viability of either a 'Boris Bridge' or 'Boris Burrow', as the potential projects have been branded.
But an area of the Irish Sea called Beaufort's Dyke - where tonnes of surplus military munitions and radioactive waste have been dumped over the decades - has caused most concern.
It was originally reported that the amount of munitions dumped was around 100,000 tonnes, but now a former BBC journalist has shed new light on the actual volume of material on the seabed.
Alex Kirby, who was the BBC's Environment Correspondent from 1987 to 1995, said he first reported on the existence of the munitions dump almost 30 years ago.
The Ministry of Defence (MoD) informed him at the time that it had dumped munitions there since end of the Second World War.
The MoD said around 100,000 tonnes of material had been discarded in Beaufort's Dyke.
In a letter to the Guardian, Mr Kirby said that, some months later when British Gas were planning on building an undersea pipeline in the area, the MoD contacted him with an update.
"It had been using the dyke since the end of the First World War, it said. It did not know what munitions were down there, but the total was about a million tonnes.
"I'd fancy my chances of crossing the North Channel in a tunnel as little as on a bridge," Mr Kirby said.
In order to get round this problem, it was reported at the weekend that Boris Johnson is considering proposals that would involve three tunnels from Great Britain converging under a "giant roundabout" beneath the Isle of Man, with one tunnel continuing to Northern Ireland.
The Sunday Times reported that the three proposed routes from Great Britain would start at Stranraer, Heysham and just outside Liverpool.