The animals have used Orford Ness as a breeding ground every year since 2021, according to rangers, and this season alone 130 pups have been born.

The group have become Suffolk's first breeding grey seal colony, having likely spilled over from well-populated colonies in Norfolk.

In the wild, it is common for seals to return to the same place each year to give birth.

Matt Wilson, countryside manager for the National Trust's Suffolk and Essex Coast portfolio, said rangers had conducted weekly seal counts at the former military site since the start of October, averaging more than 250 adult seals per week, and sometimes up to 500.

He said he thought part of the reason the colony had remained there was due to the remote nature of the site and lack of disturbance.

Orford Ness was used as a military test site during both world wars and into the nuclear age, before the Ministry of Defence sold it to the National Trust in 1993.

During the COVID pandemic the site was closed for an extended period, meaning visitor access was significantly reduced.

The site is also closed between October to March, which coincides with the grey seals breeding season.

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"We understand that people will want to see the colony now they know it's here, but it's important we continue to limit disturbance, to give the pups the best chance of survival," Mr Wilson said, adding that guided tours may be offered next winter.

Glen Pearce, Orford Ness's property operations manager, added: "Since the seals' arrival in 2021, our team of volunteers and staff have monitored the seals from a distance, keeping the growing seal colony a secret.

"However, the colony has now grown to a size where we want people to share this amazing wildlife success story with our supporters, but also to advise visitors how they can help us protect the colony.

"Unauthorised access, by foot, boat or drone, is illegal and also dangerous because of the unique and remote nature of the former military site."