A former Suffolk policeman has admitted stealing nearly 650 wild bird eggs, including more than 60 from some of the rarest species in the UK.

Michael Upson amassed the collection – which included eggs from the wood lark, Cetti’s warbler and marsh harrier – over a 10-year period while working for Suffolk Constabulary.

He developed a sophisticated indexing system detailing how and when he found each egg, which was discovered by police, along with egg blowing drills, when they searched his home in Sotherton, near Halesworth, in June.

Upson, a father of two, will be sentenced today after pleading guilty to two charges of possession of eggs before Norwich magistrates yesterday, contrary to the Wildlife and Countryside Act 1981.

The court was told the 52-year-old amateur ornithologist would have had a “significant impact on the species” and the environment in the Dunwich area, where he found many of eggs.

Mark Thomas, senior investigator for the RSPB, called the case “shocking” and said outside court that Upson had also travelled the UK to “systematically target some of the country’s rarest birds”.

“Norfolk and Suffolk are hotspots for wild birds and the police and the RSPB and other organisations work together to protect these birds.

“He was in a position of authority and trust and he broke that – he broke it for over 10 years,” said Mr Thomas.

The 53 wood lark eggs Upson had in his collection were taken at a time when there would have been only 500 to 700 pairs in the UK, he said.

“They are extremely well camouflaged on the ground, and it would have taken hundreds of hours to find these nests,” he added.

Prosecutor Judith Piggin told the court that officers found the eggs hidden in suitcases which had been “secreted” in towels in an airing cupboard, when they executed a warrant on June 21.

The officer, who has since retired, made full admissions to police but said the collection had been made between 1991 and 2001, and he had not looked at them for many years.

A total of 649 wild bird eggs were found stored in margerine tubs, including 65 particularly rare eggs, defined as Schedule 1.

A log book detailing the circumstances of each egg find was found stored in a water tank by police.

Miss Piggin said: “He admitted all the eggs found were his, and that it was his collection. He also admitted all the connected items seized and the kit found in the airing cupboard was his too.”

Roger Thomson, mitigating, said the collecting had been the result of “a mad period” in the 1990s for Upson, during which he had been having marital troubles and suffering from depression, but that he knew his actions were wrong.

He denied that his client, a “keen naturalist and ornithologist”, had ever taken eggs while on police duty and said he had served the community for many years.

Mr Thomson said: “The collection has been gathering dust in the attic. It’s been up there and he has not shown it to anyone else.

“He wishes now that he had just thrown it away but he found it difficult.

“He knew it was wrong to have them in the first place and thought it would be more wrong to have thrown them away.”

Magistrates will also rule today whether Upson’s diaries, maps and more recent photographs can be returned to him.