Police cordoned off the area but delayed entering the house

Frank Mullane's sister Julia Pemberton and nephew William, 17, were murdered at home in Berkshire in November 2003.

Mr Mullane, from Swindon, met with Home Office minister Baroness Scotland on Thursday morning.

The minister said she would speak to the chief constable of Thames Valley Police about Mr Mullane's concerns.

This police force in my opinion needs the biggest kick up the backside possible to propel them into the future Frank Mullane

Mrs Pemberton and her son were shot dead by her husband Alan at their luxury home in Hermitage, near Newbury, before he turned the gun on himself.

The family are calling for a homicide review to be held into the tragedy - a new multi-agency procedure designed to learn the lessons of such events.

Mr Mullane, who was accompanied to the meeting by his sister's daughter, Laura, 20, believes the deaths could have been prevented.

Mrs Pemberton was known to police as a victim of domestic abuse.

At the time of the shooting, there was a delay of several hours before police entered the house.

An inquest in Reading in 2004 heard the transcript of a 16-minute 999 call in which Mrs Pemberton describes how her husband was moving through the house getting closer and closer to the cupboard where she was hiding.

Mrs Pemberton was heard to say: "I've got about one minute before I die," shortly before Alan Pemberton shot her.

Alan Pemberton killed his wife and 17-year-old son

Standing hand-in-hand with his niece, who was away at Cambridge University on the night of the killings, Mr Mullane said: "This police force in my opinion needs the biggest kick up the backside possible to propel them into the future."

He said the minister had said she would have a conversation with Thames Valley Police's chief constable Peter Neyroud and that she would be following this case.

Mr Mullane added: "It's a high level response, it means that we can go away and breathe for a few hours and see what is the next step.

"But if it doesn't happen, believe me, it's only round one."

He said he would be "watching the reaction of the police" and added: "This is a matter of life and death, it's not profit and loss, and errors are irreversible."