Blair Logan poured petrol on his younger brother Cameron, 23, and Rebecca Williams in bed as they slept at the family home in Milngavie, East Dunbartonshire, in the early hours of 1 January.

The couple had been at a New Year’s Eve party and had walked to the family home before the fire was started at 7.25am.

Ms Williams was taken to hospital after being rescued by her boyfriend’s father and neighbours who rushed to help.

Logan’s parents David and Catherine were treated for smoke inhalation.

The family dog, Gomez, was also killed in the fire.

Logan pleaded guilty to a charge of murder and attempted murder at the High Court in Glasgow on Friday.

He has been subject to two psychiatric reports which concluded there was not sufficient evidence for a plea of diminished responsibility.

He was also charged with endangering the lives of his parents, who were in the court room along with Ms Williams, as the guilty plea was made.

Logan was said to have had a “hostile relationship” with his brother and the attack was said to be in retaliation for a recent incident at the house when his brother had punched him.

Searches of Logan’s computer revealed he had researched burn injuries.

After his arrest, Logan told detectives he took the petrol from a church garage six weeks before the fire and kept it in his bedroom, but said: “I didn’t want to kill him”.

Alex Prentice QC, prosecuting, said Logan admitted pouring petrol “with the intention of maiming or crippling” his brother.

Defence lawyer Shelagh McCall said Logan showed “wicked recklessness” but did not intend to kill his brother.

He was said to have “felt physically sick at the whole thing”.

Ms McCall said there were “unusual traits” in Logan’s personality and that he had a lack of understanding of the impact of his actions on other people.

Logan will be sentenced on 11 August.