Dr David Mackereth’s 26-year medical career hasn’t been jeopardised by endless, gruelling, night shifts.

Nor have the life and death decisions he has made on NHS emergency wards for decades put him off his profession.

It was, in the end, his response to an instruction in a nondescript training room that has left his future hanging in the balance.

After being offered a job as a medical assessor for the Department for Work and Pensions (DWP), David was told to refer to those seeking disability allowance as whatever gender they requested.

Dr David Mackereth was fired by the Department for Work and Pensions for saying people can't choose their gender

So, should a man have walked into his office claiming he was a woman, he would need to be treated as such, and described in any correspondence with the pronoun ‘she’ not ‘he’.

In an age in which the Government and the NHS are subjecting transgender issues to ever greater scrutiny, it was an edict that David had been dreading — and one the 55-year-old was unwilling to obey.

‘As a Christian, I believe gender is determined biologically and genetically,’ he says.

He was also very aware that expressing such a belief would be likely to end his career.

‘I was scared, really frightened,’ he admits. ‘I knew it could be the end of my work as a doctor, but I could not live with myself if I didn’t speak up. It would be dishonest — and I didn’t want to live a lie.’

Sure enough, his contract with the DWP was swiftly terminated on the grounds that his refusal to use the preferred pronouns of people who identify as the opposite gender could be considered harassment as defined by the 2010 Equality Act.Three weeks on, he is in little doubt that his career is over.

‘I can’t get a job with any other Government department — doors will be slammed in my face — and I don’t think the NHS will employ me again,’ he says.

‘I am hurt, but relieved I said what I said, because I believe with all my heart that God made us male and female and that I should be allowed to believe this.’

His strong opinions on one of the most divisive subjects of our times are, he insists, not the only issue here. What is also at stake is our right to say what we think without risking our jobs.

‘It is not a question of whether we agree or disagree but whether we are free to say so,’ he says.

‘I’m not out to upset anyone. I care deeply about transgender people. But we must be able to say what we think, and defend what we believe in a non-combative way. Otherwise we will turn into a dictatorial state in which we are all enslaved.’

An unassuming man who relaxes by reading history books and growing tomatoes in his garden in Dudley, West Midlands, David has emerged as an unlikely figurehead for freedom of speech since his ordeal made the news this week.

He fiercely guards his privacy, refusing to divulge any information about his wife and four adult children. He admits he is terrified his unfashionable views may result in him being ‘lynched’.

Perhaps he has good reason to be nervous, given our censorious age in which anyone who dares to deviate from the fashionable consensus that gender is a social construct, not a biological fact, risks being demonised.

Since transgender rights have come to the forefront of public discourse, David says among NHS colleagues a ‘climate of fear’ has emerged regarding new protocols.

Doctors, for example, are now advised by the British Medical Association to use the term ‘pregnant people’ to avoid causing offence to transgender individuals. And, from next year, Government guidelines could require GPs to ask patients’ sexual orientation before each appointment to avoid discrimination.

David, pictured with fellow Christians, has worked for the NHS for 26 years but has been told he cannot be employed by the Department for Work and Pensions because he doesn't agree that people can self-define their gender

Meanwhile, proposed changes to the Government’s Gender Recognition Act would mean people could easily identify as the opposite sex without the need for medical diagnosis. All of which horrifies David, who believes that not only will such measures cause untold psychological harm to patients, but that an already stretched NHS will be pushed to breaking point.

‘There is very little talk between staff these days because none of us knows what the rules are,’ he says. ‘We are trained to inform on another doctor if they are unfit to practise and no one wants to get reported.

‘There is a belief we cannot say what we think in case we get accused of harassment. Nurses coming across patients with male genitalia on female wards have whispered to me that the situation is wrong.

‘Some of my colleagues — senior doctors — are fired up by what happened to me, but what am I supposed to say to them?

‘After all, if they say the same thing as me, will the country start losing much-needed, remarkable surgeons who are no longer considered fit to work because they used the wrong pronoun?’

When David arrived at St Andrews University in Scotland in 1981 to study medicine, things were very different. ‘There was no question of any possibility that gender was mutable,’ he says. ‘Transgender people would have existed, but somehow we all managed to get along.’

Dr Mackereth pictured when graduating university in 1988

He became a Christian after his first term at university, when he met a religious medical student. He says his conversion made him even more resolute on the biological determinism of gender.

‘I am clear in my own mind what the Bible teaches on gender,’ he says. ‘In the beginning, God made them male and female.’

While some believe overt spirituality can be at odds with a science-based career, David, who finished his medical training in Manchester, where he met his wife of 30 years, insists both put him in a position to ‘serve.’

He says: ‘People ask why I have to bring Christianity into my argument when I can prove my point with science. I think the scientific argument is conclusive but in itself isn’t powerful enough. We are taught a relativistic world view in which there is no absolute truth.

'We cannot deal with relativism without introducing philosophy or Christianity.’

David carved out his career as a locum junior doctor in numerous accident and emergency wards throughout England, Wales and Scotland, and for the past seven years has worked mainly in A&E at the Princess Royal Hospital in Telford, Shropshire.

He believes that once same-sex marriage became legal in 2014, attention was turned to the next gender-related issue.

‘Suddenly, transgender issues became “British values”,’ he says. ‘If you tell a six-year-old boy they could be a girl, of course they’re going to be confused.’

Does he not believe a small minority of people are simply born into the wrong body? ‘I’d want to speak to them before answering that question — and I would be willing to,’ David says.

He is adamant that transgender people are themselves victims of a darker agenda driven by global forces seeking to obliterate gender differences altogether.

He cites Facebook, which in 2014 introduced 71 gender identification terms ranging from asexual to intersex and polygender.

He also references George Orwell’s 1984 and its uncannily prophetic premise of a totalitarian state and its systematic eradication of words and their meanings.

David believes gender ideology is so dogmatic we are edging ever closer to a similar environment. ‘Once we no longer have gender, we are all the same,’ he says. ‘Ruling powers can control us. It is a way of enslaving us all.

‘If we cannot call pregnant women pregnant women, and must call them people, we have reached the stage of saying two plus two is five, and black is white, and we are slaves.’

He points out the NHS comprises not only many Christians but huge numbers of Muslim doctors, many of whom feel similarly uncomfortable with the subject of sex change on account of their religion.

‘Are they going to take all these doctors and nurses to one side and sack them? There’d be no NHS left,’ he says.

The doctor said he believes transgenderism is 'relatively rare' and has only treated one patient during his career

He reveals that in the course of his medical career, he has knowingly treated only one transgender patient, a transgender female two years ago.

He says this supports his belief that transgenderism is relatively rare. In the case of this one patient, he says, he was able to get by without using any pronouns at all: ‘I found it very difficult but of course didn’t say anything . That wouldn’t have been appropriate.’

A combination of a heart condition that makes him tire more easily and a desire to help disabled people claim the benefits they are entitled to prompted David to apply in May this year for the position of disability allowance assessor for the DWP.

He was recruited by APM, an employment agency, and sent for two weeks of training in London alongside four other doctors.Two days into his second week of training, the doctor instructing the group of five announced they must use the pronoun requested by the client in spoken discussions and all written correspondence.

Many might argue that for the sake of a couple of words, it might have been worth keeping his feelings to himself — but David insists the pronouns ‘he’ and ‘she’ are profoundly significant. ‘They stand for who we are, and how we relate to each other,’ he says.

He can see how a transgender person might be offended if they were referred to as a gender they no longer belonged to, but insists it would have no bearing on the quality of his work.

‘People could say “He’s not treating people with respect” — as if respect means you agree with everything somebody says to you. It doesn’t. It means I will disagree but will still give the same standard of care.’

After voicing his objections, David was referred to APM’s manager who called him into a meeting the following week after he had started his new job at offices in Birmingham.

‘He asked, “If a man asked him to call you Mrs, would you do it?” I said I couldn’t. If somebody has male XY chromosomes and male genitalia I cannot in good conscience call them a woman. We agreed I wouldn’t come into work until the DWP had decided what would happen to me.’

Several days later, his manager emailed to say that as David had refused to use pronouns in the way required, he was breaking the law, could be harassing people and, therefore, his contract was terminated.

‘I was devastated,’ admits David. ‘I’m passionate about being a good doctor, and even if I disagree with someone, I don’t want them to come to any harm.’

He has written to the agency which hired him as a locum doctor, but holds out no great hope he will be allowed back into NHS emergency wards. ‘The people I worked with will be afraid to be seen talking to me,’ he says.

He has read a lot of ‘nasty’ comments about him online and admits that if he doesn’t find work soon ‘the pennies will run out’.

But, despite all this, he doesn’t regret his decision: ‘The DWP has dispatched not just Christianity, but some enormous world views as if they don’t exist. I am prepared to make a bold stand because freedom of speech is a critical issue to all of us. We have to be able to say what we think.’

A DWP spokesperson told the Mail Mr Mackereth made it clear in training that he would refuse to use pronouns which did not match his own view of a person’s biological gender and that the Equality Act made it unlawful to discriminate on the grounds of a ‘protected characteristic’ such as gender reassignment. She added: ‘We expect all assessors to handle assessments sensitively and adhere to the Equality Act 2010.’

Both APM and the NHS declined to comment.