Carla Risoldi, a student at the University of Cambridge in 1985, has returned her old room key to Gonville & Caius College 40 years later.

The College waived a potential £20,000 fine after Risoldi, who studied as an American exchange student, returned the room key she accidentally took home.

Risoldi attended a six-week course at Cambridge in 1985, while studying at the University of Pennsylvania. At the end of her visit, Ms Risoldi forgot to return her key and inadvertently took it back to the USA.

On a trip to the UK 40 years later, the former student finally returned the key to the Caius Porters’ Lodge.

Caius told the BBC that failure to return a room key would usually involve a £10 outright fee, with an interest of £10 a week.

Ms Risoldi would therefore, in theory, have incurred a £20,850 fine for the missing key.

However, after the former student returned the key, the college shared that “the fine – to cover the cost of cutting the key – and any associated interest – was waived on this occasion”.

The use of traditional room keys has long since been abandoned at Caius, with physical keys, such as Ms Risoldi’s, now replaced by CAMcards. John Turton, the senior porter on shift, presented Ms Risoldi with the retired key as a memento.

Now an attorney, Ms Risoldi has positive memories of the summer school, organised through the University of Hampshire: “It opened up my eyes – I had never been anywhere.”

Explaining their reasoning for not enforcing the fine, Caius said it “of course, was not enforced – we’re quite friendly here”.