International lawyers have advised the family of slain journalist Daphne Caruana Galizia that the murder investigation is in clear breach of the European Convention of Human Rights.

The family had objected to the fact that police deputy commissioner Silvio Valletta was heading the murder probe. Mr Valletta is married to Gozo minister Justyne Caruana, both of whom were criticised by Ms Caruana Galizia before she was murdered on October 16.

In a statement, lawyers at Doughty Street Chambers in the UK said "we are of the firm view that Malta is in flagrant violation of the Article 2 investigative duty and thus in breach of its obligations under the ECHR". 

READ: Government calls law firm's opinion 'completely one-sided' 

They added that from the information available at this stage it appeared highly likely that the Maltese authorities had also violated other human rights of Ms Caruana Galizia and the bereaved family.

The lawyers’ legal opinion called for swift action to be taken by the authorities in Malta to immediately remove the deputy commissioner from his role and to apologise to the family "for the failure to appropriately update and involve them in the investigation, and alter the way in which information is provided to them".

They further noted that the involvement of external, impartial investigators was “an essential requirement, and an extremely urgent one.”

Last month, Ms Caruana Galizia's husband and children instituted constitutional proceedings against the Police Commissioner, the Attorney General and the deputy commissioner.

They claimed his involvement in the investigation could breach their right to a fair hearing.

Three men were charged with the journalist's murder last Tuesday.