John Barrett had a history of mental health problems

John Barrett, 42, stabbed Dennis Finnegan as he cycled through Richmond Park, south-west London, in September.

He was given a life term and told it would be at least 15-and-a-half years before he was considered for release. That has been cut to seven years.

The victim's brother John Finnegan says the family is appalled by the decision.

Mr Finnegan said: "It has come as bit of a shock really that they could reduce the sentence by half without any acknowledgement to the family. It's very strange.

'Slip rule'

"I think that the illness the guy [Barrett] has got is a life-long illness and therefore if he can't control it, which obviously he can't, then he should serve the sentence he's been given in court."

Barrett, 42, from Putney, south-west London, admitted manslaughter on the grounds of diminished responsibility.

It is understood that the case was brought back to court, where the judge cut Barrett's sentence to seven years under the "slip rule", after reviewing the tariff at Lewes Crown Court.

A Home Office spokesperson said: "The slip rule allows a judge to change his sentence within 28 days of the first sentence if he has the agreement of the prosecution and defence lawyers.

"This means that if an error has occurred in sentencing the judge can correct it rather than letting the case go to the Court of Appeal."

Mr Finnegan was cycling in the park when he was approached by Barrett who stabbed him several times in the back and chest before walking off.