An HS2 archaeological dig has uncovered one of the best persevered 16th century ornamental gardens ever discovered in England, rivalling those of Henry VIII’s Hampton Court Palace.

The site of once-sprawling flower beds and gravel paths, uncovered to the east of the Birmingham section of the high-speed line, are comparable in size to the Elizabethan gardens of Kenilworth Castle.

The shape of what was once Coleshill Manor and a well-defined octagonal moat were originally picked up by air photography, during a site assessment of the rail route.

As excavations continued, the remains of a massive garden dating from the decades either side of 1600 were discovered, alongside an impressive manor house.

The house was owned by Sir Robert Digby and experts now believe that after marrying an Irish heiress, he built his home in the modern style, along with huge formal gardens measuring 300 metres (984ft) from end to end, to show off his new wealth and status.

Entirely unknown before, the preservation of the gardens has been described as exceptional, with paths, planting beds, garden pavilion foundations and ornaments organised in a geometric pattern.

Jon Millward, HS2’s historic environment manager, said: “It’s fantastic to see HS2’s huge archaeology programme making another major contribution to our understanding of British history.

“This is an incredibly exciting site, and the team has made some important new discoveries that unlock more of Britain’s past.”

Stuart Pierson, project officer for Wessex Archaeology which carried out the dig, said it was a “once in a career opportunity” to work on such a site, with a history that spans 500 years.

“Evidence of expansive formal gardens of national significance and hints of connections to Elizabeth I and the (English) Civil War provide us with a fascinating insight into the importance of Coleshill and its surrounding landscape.”

He added: “From our original trench evaluation work, we knew there were gardens, but we had no idea how extensive the site would be.

“As work has progressed, it’s been particularly interesting to discover how the gardens have been changed and adapted over time with different styles.

“We’ve also uncovered structures such as pavilions and some exceptional artefacts including smoking pipes, coins and musket balls, giving us an insight into the lives of people who lived here.

“The preservation of the gardens is unparalleled.

“We’ve had a big team of up to 35 archaeologists working on this site over the last two years conducting trench evaluations, geophysical work and drone surveys as well as the archaeological excavations.”

Dr Paul Stamper, a specialist in English gardens and landscape history and a visiting fellow in English local history at the University of Leicester, said: “This is one of the most exciting Elizabethan gardens that’s ever been discovered in this country.”

He said the preservation was “exceptional” and would add to the knowledge of gardens of the era.

“There have only been three or four investigations of gardens of this scale over the last 30 years, including Hampton Court, Kirby in Northamptonshire and Kenilworth Castle, but this one was entirely unknown,” he added.

“The garden doesn’t appear in historical records, there are no plans of it, it’s not mentioned in any letters or visitors’ accounts.

“The form of the gardens suggest they were designed around 1600, which fits in exactly with the documentary evidence we have about the Digby family that lived here. ”

The hall came into the hands of the Digby family in the late 15th century, with the new owner developing the existing hall, creating a deer park and the laying of the formal gardens in the 1600s.

Excavations have revealed earlier structures, dating to the late medieval period, including a large 14th or 15th century gatehouse which was thought to have been demolished some time after 1628.