A football club manager who headbutted his sister’s partner at his own birthday party has been jailed.

Sending Luke Brennan to prison for 14 months, Judge Peter Crabtree said: “This was a brutal attack when you were intoxicated in which you headbutted your victim and followed through with two punches, causing him serious injuries that have had an ongoing impact upon him.

“The only sentence that is appropriate to reflect the seriousness of that offence is an immediate custodial one.”

Earlier, prosecutor Simon Foster told Swindon Crown Court Brennan, 34, had been celebrating his birthday on the evening of November 9, 2019, with a barbecue and bonfire party at home.

His victim, who had been in a relationship with Brennan’s sister, arrived at the party. He and Brennan were said to have argued over the man’s daughter – the defendant’s niece. Brennan asked him to leave the party.

His victim told detectives his daughter had asked if she could stay at Brennan’s home. He had gone into the garden to talk to him about it.

The argued, with other partygoers described seeing the man push Brennan to the chest during the dispute. He responded by headbutting his victim, then knocking him to the ground with another blow.

Police arrived at the party and heard somebody – although it was not clear who – say “I did nut him, but he was out of order”.

Brennan’s victim told police he didn’t want to make a complaint. He later changed his mind after he was taken to hospital by officers and realised of the seriousness of his injuries.

The court heard he suffered broken teeth, a broken nose, two black eyes and extensive bruising. The cost of the dental work was estimated to be up to £8,000. In a victim personal statement, he said the assault had affected his mental health.

Interviewed by the police, Brennan was asked who was responsible for the injuries to the victim. “I can’t remember,” he replied. Both men had drunk alcohol.

Brennan, of Beech Avenue, Pinehurst, pleaded guilty at the magistrates’ court to causing grievous bodily harm. He had almost finished a community order for unrelated offences when he committed the attack.

Defending, Emma Hillier said her client was remorseful. There had been significant delay in the case coming to court and he had not been in trouble with the police since being arrested in late 2019.

He was said to manage a football club, understood to be Swindon and District League side North Swindon FC, and helped with a mental health support group for young men. He worked for his father’s scrap metal business and rented his own home. “This incident was out of character and the two parties shook hands afterwards,” Brennan’s advocate said.

Among the references provided to the court were letters from his nieces – his victim’s daughters – who spoke of the support Brennan had provided them. The court heard Brennan’s sister and his victim had separated.

Judge Crabtree noted the mitigation in the case and the fact that any prison sentence served during the coronavirus pandemic would be more arduous, but said the offence was too serious for anything other than immediate custody.

He imposed a four year restraining order banning Brennan from contacting his victim directly or indirectly.