When a Dartmouth family set out on a birthday treasure hunt treat the last thing they expected to find was real treasure – dating back to battling King Henry V.

But that is exactly what Mathew and Emma Cusack did when they and their two children went exploring the beach at Slapton with their son's 11th birthday present – a metal detector.

They had come up with a few corroded pennies and two pence pieces when Mathew spotted what he thought was a shiny cap to a wine bottle with the vineyard's crest on it.

For fun he buried it while Emma had a go at finding it again with the metal detector – which promptly went 'barmy' Mathew told a Treasure Trove inquest.

When he picked it up again he quickly realised it was gold. And, within minutes the family had found a second coin.

Matthew told the Torbay coroner: 'We spent an awful lot of time going up and down the beach, but that was that.'

The treasure trove turned out to be a pair of gold quarter Nobels dating back more than 600 years and worth something like £500 to £700 each. But they are both now likely to end up in Plymouth Museum after the coroner decided they officially belong to the crown.

However, Mathew and Emma could end up being given a small reward for handing in their treasure.

And Mathew revealed after the inquest that there is also an outside chance that if the Plymouth Museum decides it does not want to shell out for the two coins, they could be given back to him.

If that happens he plans to hand them to Dartmouth Museum so that they can go on display to the public.

'It would be great to be able to see them on show publicly and that we would be able to go along and see them. They were found locally and it would be nice to keep them local.'

The unusual treasure trove inquest went ahead at Torquay in front of Torbay and South Devon Coroner Ian Arrow.

Mr Cusack, who lives in Yorke Road, Dartmouth, and his family had been walking the beach below the middle car park on Slapton Line in February 2011 when they found the coins.

He said his son had been given the metal detector for his 11th birthday and they had been using it up and down the beach.

'We spent about 45 minutes picking up 2p and 1p coins when I spotted what I thought was the top of a wine bottle with a shiny crest.

'I decided to bury it in the sand to see if my wife could find it. When she did the metal detector went barmy. On closer inspection it looked like a coin and when I cleaned it up it was really shiny and bright. Everything else we had found had been very corroded.

'We walked along the shoreline a few paces and there was another one.'

Coroner Ian Arrow heard that the date of the find was probably February 19, some time around lunchtime when it would have been a low spring tide.

As the family found the coins on the water edge below the mean high water mark it meant that the find was not on private property and would therefore belong to the crown.

One of the coins they discovered dated from the One Hundred Years War with France and was dated 1361 – 1363. The second was minted in the reign of Edward's grandson Henry V, of the Battle of Agincourt fame, some time between 1413 and 1422.

The Cusacks handed their find into the Portable Antiquities Scheme after checking out the coins on the internet.

Danielle Wootton from the scheme told the inquest the coins had been researched by the British Museum.

They will now go to the Treasure Evaluation Committee to find out how much they are worth and Plymouth Museum has said it is looking at buying them.

'They are really interested in seeing them go on display,' she said.

Mr Arrow told he inquest he was satisfied that the coins constituted 'treasure' under the 1996 Treasure Act and that it belonged to the crown estates.

He said he would also be informing the Receiver of Wrecks of the location of the find 'in case anyone else wants to conduct a search'.