The two teachers and a pupil who were hurt in a stabbing at a school in South Wales have been discharged from hospital, police have said.

It comes as the brother of the teacher who helped restrain the girl accused of attacking the teachers and a fellow pupil said he “does not think of himself as a hero”.

The victims were injured at Amman Valley School in Ammanford, Carmarthenshire on Wednesday morning and a teenage girl was arrested on suspicion of attempted murder and remains in custody.

One of the teachers injured in the attack has been named as Fiona Elias, the head of Year 7, by Prime Minister Rishi Sunak’s official spokesman.

The second adult is reported to be Liz Hopkin, a special needs teacher.

The spokesman said the Prime Minister’s thoughts are with those injured and offered praise for staff and students for responding so calmly and bravely to the incident.

While online lessons will continue, the school will stay closed for in-person teaching on Friday, Carmarthenshire County Council has said.

A council spokesperson said that Dyfed Powys Police believe they are likely to conclude their investigation at the school by the end of the day on Thursday.

Whether the school will reopen on Monday has not been confirmed.

A Dyfed-Powys Police spokeswoman confirmed on Thursday that the victims have now been discharged from hospital.

Carmarthenshire Superintendent Ross Evans said: “As can be expected with an incident as serious as this, there will continue to be a police presence at the school throughout the day today.

“Officers at the scene will be looking for evidence to assist the investigation, while other specialist teams will analyse any information submitted through our dedicated web page.

“We understand the level of concern in the community as people try to process the incident.

“We urge anyone affected by yesterday’s events to seek support, and not to share any videos, photos or information that might cause further distress to pupils or parents at the school.”

A teenage boy was arrested overnight on suspicion of making threats which referenced the stabbings at the school, Dyfed-Powys Police said.

Police executed a warrant at the boy’s home, in the Cross Hands area, and recovered a BB gun.

Mr Evans said the investigations were being dealt with separately but added that “officers will be seeking to establish both the credibility of the threats, and whether there was any connection between the alleged offences”.

Darrel Campbell, the teacher who restrained the alleged Ammanford school attacker, does not think of himself as a hero, his brother has insisted.

Mr Campbell disarmed the alleged attacker and put her in an armlock ahead of emergency services arriving at the school.

Speaking to the PA news agency, Cefin Campbell, the Senedd member for Mid and West Wales, said: “He’s embarrassed by all the attention that he’s had, he certainly doesn’t consider himself a hero in any way.

“He just told me he just did what most people would have done – he acted instinctively, he saw the danger and took action.

“He really wants to play down anything more than just being a normal citizen, albeit a teacher in a school facing a very challenging situation.”

Darrel Campbell, who has worked at the school for around 40 years, officially retired last year but was brought back on a part-time basis to help provide pastoral care.

Both he and his brother attended the school as pupils.

Cefin Campbell said he expects his brother will return to work when the school reopens.

He probably did what most people would have done in the same situation, try to calm things and restrain people from making the situation worse

He said: “The school is closed today so he’s off but he has every intention of going back whenever the school reopens.

“He wants to be there, with the other staff members, to support each other and to support the pupils that are under their care.

“He’s taken that role very seriously throughout his life and he will go back to make sure that the pupils are in a good place.”

Speaking on BBC Radio Wales, the politician said: “He’s been a teacher there for 40 years and he was involved in the incident yesterday in the sense that he was the first at the scene and he obviously had to deal with a very distressing and chaotic situation.

“He probably did what most people would have done in the same situation, try to calm things and restrain people from making the situation worse.

“Obviously, he’s been shaken by the whole experience as have all the staff, pupils, parents and so on.

“But I think it’s the sense of shock because he’s been there for 40 years as teacher, he’s never ever seen anything like this.

“I think that hits home to people that it should happen in a place like this.”

The south-west Wales school went into lockdown after a “code red” alarm sounded through the PA system, during which students and staff are said to have hidden in classrooms – with one pupil reportedly vaulting the school fence to get to safety.

The lockdown lasted around four hours between 11.20am and 3.20pm, resulting in a lengthy and anxious wait for parents who were seen tearfully hugging their children after they walked through the gates.

Footage of the incident has been circulating online, with a number of newspapers reporting the contents of one video in which a panicked pupil can be heard shouting about someone getting stabbed.

Mr Campbell said there would be questions asked in the Senedd about security in schools across Wales.

“Let’s hope it’s a one off, but you just don’t know the way the society has changed. We have to ask questions about the way we move forward,” he told BBC Radio Wales.

“We certainly don’t want to go down the route of America but there are parts of the UK where bags are checked every day, there’s metal detectors, as well as random checks by police.

“None of us want to go down that road but we’ve just obviously got to ask questions. What lessons can we learn from this?”

All three victims were taken to hospital with stab wounds but Dyfed-Powys Police said their injuries were not life-threatening.

The force also said a knife has been recovered.

Amman Valley School – a bilingual comprehensive school for pupils aged between 11 and 18 – will not open on Thursday to allow police to continue their investigation.

It is also known as Ysgol Dyffryn Aman and is maintained by Carmarthenshire County Council and provides education to 1,450 school pupils, in addition to 270 sixth form students.