It is a sunny day in Norfolk and Peter Prinsley, the first Labour MP for Bury St Edmunds and Stowmarket, is about to look up the nostrils of a 90-year-old man. But before he can get out his microscope to look for the cause of the man’s chronic nosebleeds, his patient has something to say.

“Congratulations on your appointment!” says Tony Wilkin, as he lies down on the examination bed in Prinsley’s consultation room at James Paget university hospital in Great Yarmouth.

Wilkin’s wife, Vera, has a question: does Prinsley – an eminent ear, nose and throat (ENT) surgeon – really have the time to be in parliament when the orifices of East Anglia need him? Her husband was declared an “urgent” case in May, and he is only now being seen, in August.

Prinsley never really expected to be fielding questions from his patients about why it would now be even harder to get an appointment with him.

“The honest truth is that I was hoping to win, but in my heart of hearts, I didn’t really expect to win, because [Bury St Edmunds] was, I think, the third safest Conservative seat in England,” he said shortly after his shock victory.

Some may think Prinsley would be of more use to society in the NHS than in parliament, since he also trains the next generation of ENT surgeons and runs a genetics programme at the University of East Anglia.

But “both of these roles have their uses”, he says, with mischievous eyes behind wire-rimmed glasses. “I’ve been in that group of doctors who have often been moaning about the situation that we’re in. And a lot of people have said to me: ‘Well, if you’re moaning so much, why don’t you go and get elected and try to change things?’”

Prinsley didn’t even apply to be the candidate in Bury St Edmunds, which had been solidly Tory for 150 years. He wanted to represent Great Yarmouth, but Labour chose someone else (a decision the party’s decision-makers may now regret, after their chosen candidate ended up losing to Reform UK).

The day after Rishi Sunak called the election, Prinsley received a phone call from Labour HQ saying: “Congratulations, you’ve been selected as the candidate for Bury St Edmunds.”

With minimal help from Labour high command, Prinsley credits a gaggle of “indefatigable local ladies” for delivering his historic victory. He bought an old Post Office van, decorated it with photographs of himself in surgical scrubs, and spent the six-week campaign knocking on doors with the guaranteed conversation starter: “I’m Peter from the hospital.”

Bury St Edmunds’ last Tory MP, Jo Churchill, retired with a majority of almost 25,000, the seat deemed so safe that Sunak’s deputy chief of staff, Will Tanner, was parachuted in at the 11th hour. And yet Prinsley defeated Tanner by 1,452 votes.

At 66, Prinsley is one of the older first-timers in a parliament where 335 out of 650 MPs are new. “You know, when you go to the Houses of Parliament, the most amazing thing is how young everybody looks,” he tells his nosebleed patient. “You walk in there and you think: who has put the children in charge of the country?”

He names no names, but one of his young colleagues is 24-year-old Josh Dean, a student who was still living at home with his mother when he became the first Labour MP for Hertford and Stortford.

Moving out is a priority, says Dean, clutching his new parliamentary iPad on the Commons terrace, shortly after winning a surprise majority of 4,748. Not only does he want his independence, but he has concerns about his mother and younger brother.

“Obviously, I’m worried, because there’s security things that go along with being an MP. My brother’s 15. He’s just at an age where he’s hanging out with his friends, and his friends will all have had my leaflet through their letterbox, so I know that they know who I am, and I worry about the effect that will have on him and on my mum,” he says.

Dean left school at 17, “directionless”, and went to work in his local Starbucks, before finding his way back to education as a mature student.

He was in his final year of a politics and international relations degree at the University of Westminster when the election was called and he cannot graduate until he finishes his dissertation – a comparative study of the technologies of control used in the “war on terror” and the Troubles in Northern Ireland.

He insists most constituents do not remark on his age – though one woman told him: “God, you look about 12!” – and that he has enough life experience to be an MP.

“I didn’t go the traditional route into parliament, or through school or through work. And I think that diversity of experience is really valuable, actually.”

While Dean and Prinsley made history as the first Labour MPs for their constituencies, Abtisam Mohamed, the new Labour MP for Sheffield Central, was breaking different records. As the first Arab woman to be elected to parliament, as well as the first Yemeni, her victory made headlines far beyond the Steel City.

One of the first calls she fielded after winning an 8,286-majority came from Yemen’s answer to 10 Downing Street, with the country’s president, Rashad al-Alimi, ringing to offer his congratulations.

When the Guardian meets Mohamed in parliament, she is rushing between induction sessions, trying to get her head around the arcane traditions of the place. She is itching to give her maiden speech and cannot quite believe that, to give it, she isn’t simply given a date and time slot, but has to “bob” up and down to catch the speaker’s eye.

Not quite 5ft tall, she is at a distinct disadvantage, and has not yet managed to speak in the chamber, despite frantic bobbing: “The first time I did it, I felt really silly doing it. You just feel like a bit of a child, but it’s process, and apparently, if you don’t do it, you’re not going to get called.”

Her main priorities in parliament will be the climate agenda, supporting public sector workers and improving regional transport, she says.

Born in Yemen in 1980, Mohamed was brought as a toddler to Sheffield, where her father and grandfather worked in the steel industry.

She herself worked in the voluntary sector and as a teacher before going on to do a law degree and opening her own human rights and asylum practice in Sheffield.

She spent the summer recess closing down her office, after Starmer banned his MPs from having second jobs – with a few exceptions, such as medics, which is why Prinsley will still be doing the odd surgery alongside his new day job.

He hopes to be able to influence health policy, but disagrees with the health secretary, Wes Streeting, who declared on his first day in the job that “the policy of this department is that the NHS is broken”.

Prinsley sees it as “a bit broken, but it’s not really completely broken. I think that is something of a hyperbole.”

The new Labour intake faced their first official test of party loyalty just days into the job when the Scottish National party introduced an amendment to the king’s speech that called on the government to scrap the two-child welfare limit.

Seven Labour MPs defied the Labour whip and were immediately suspended by Starmer. None of our three newcomers were among them, though Mohamed says she too has “strong feelings on this particular issue”.

She is one of eight children, and says: “When tax credits were introduced, they were introduced by the Labour government, and it benefited families like mine.”

Would she, in her heart, have liked to have rebelled? She dodges the question like a seasoned politician: “I’m far too new to be thinking about that, and I probably wouldn’t understand the structure at this stage to be able to do it.”

On Monday, she will file back into the House of Commons after the summer recess, and bob until the speaker finally gives her the chance to speak.

Will she and her new colleagues retain their shiny optimism for changing the world? Or will they sit frustrated on the backbenches, voting for things they don’t believe in because they are frightened of what will happen if they don’t? Only time will tell.