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Police in Scotland are understood to be investigating claims Labour peer Lord Janner abused a boy there in the 1970s.

Det Ch Supt Lesley Boal said Police Scotland officers were investigating a historical complaint - but did not confirm a name.

Lord Janner was accused of abuse allegations during the 1960s, 1970s and 1980s - but was deemed unfit to stand trial in England because of dementia.

The former MP has consistently denied all allegations against him.

BBC home affairs correspondent Tom Symonds said the allegation had first been made in 1991 by a Leicester man who told police that Greville Janner sexually abused him on a string of trips across the UK during the 1970s - including in Scotland.

Police in Leicestershire investigated allegations against the politician - who represented two constituencies in Leicester between 1970 and 1997 - in the 1990s but no charges were brought, he added.

Who is Lord Janner?

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Greville Janner was born in Cardiff to a Jewish family in 1928. He served in the Army and studied at Cambridge before becoming a barrister and then QC.

He served as Labour MP for Leicester North West and then Leicester West from 1970 until his retirement in 1997, when he was made a life peer.

During his political career, he was involved in advocacy for the Britain's Jewish community and served as president of the Board of Deputies of British Jews

He was a founding partner and chairman of JSB Group Ltd, where he worked between 1990 and 1997, and he was also a non-executive director of Ladbrokes for 11 years.

Lord Janner has been the subject of several police investigations, but has never been arrested or charged. In 1991, he made statements in Parliament asserting his innocence after a man claimed he had abused him.

He was diagnosed with Alzheimer's disease in 2009. Earlier this year, Director of Public Prosecutions Alison Saunders said his condition was "rapidly-worsening".

Lord Janner, now 86, has been suspended from the Labour Party, but will remain a member of the House of Lords until his death or until he formally retires under reforms passed last year.

His family have described him as a man of "great integrity", and said he is "entirely innocent of any wrongdoing".

However Scottish police have reviewed files from the original claim relating to the alleged abuse in Scotland and are now carrying out their own investigation, our correspondent said.

"Because Scotland has a separate and independent prosecutor, it would be able to make its own decision about whether to charge Lord Janner," he added.

'Must be heard'

In a statement, the force said: "Police Scotland is conducting an investigation into an historic complaint and as such it would be inappropriate to comment.

"Police Scotland is absolutely committed to bringing perpetrators of abuse to justice regardless of the passage of time."

An NSPCC Scotland spokeswoman said: "When victims of child abuse come forward their voices must be heard.

"Police Scotland, the Crown Office and procurator fiscal must carry out a full investigation into any allegations concerning Lord Janner in Scotland and explore all mechanisms available within the Scottish legal system to ensure justice is served."

In April, the Director of Public Prosecutions in England and Wales, Alison Saunders, decided allegations against the peer by nine men were strong enough to merit a prosecution.

However, she said the prosecution should not go ahead because Lord Janner would to be unable to take part in his defence due to his poor health.

Last month, the Crown Prosecution Service, covering England and Wales, said it would review the decision. A senior prosecutor unconnected to the original case will carry out the review.

Justice Lowell Goddard - who is leading an independent inquiry into child sex abuse in England and Wales - has also said she will investigate claims against Lord Janner.

A separate inquiry was announced last month into historical abuse of children in care in Scotland. It will be chaired by leading QC Susan O'Brien.