Thousands of teachers are being lured abroad with lucrative pay packages as England's schools grapple with a recruitment crisis, Ofsted warns.
Chief Inspector Sir Michael Wilshaw says elite public schools have been opening up branches abroad, leading to a boom in international schools.
More people left the UK (18,000) to teach than trained (17,000) on English post-graduate routes, he adds.
Ministers cited figures saying just a tiny fraction of teachers left the UK.
The Department for Education also said it was disingenuous to suggest its approach to teacher recruitment was not working.
But Sir Michael's claim comes after the government missed its teacher trainee recruitment targets for the past four years.
This has led to shortages of teachers in most subject areas, and many schools are finding it hard to recruit staff.
Sir Michael said it was not surprising that the demand for UK-trained teachers was soaring as English was the most common language used in the estimated 8,000 international schools, many of which follow a British-style curriculum.
He added that the demand for UK-trained teachers was only likely to increase as the number of international schools is projected to nearly double to more than 15,000 by 2025.
He quoted International School Consultancy figures which suggested 18,000 people had left the UK to teach abroad in 2015, although he acknowledged not all of these would have been fully qualified teachers.
Recruitment agencies were actively targeting newly qualified teachers, he claimed, as well as more experienced classroom professionals - with "enticing offers of competitive, usually tax-free salaries, free accommodation and often the prospect of working in warmer, sunnier climes".
He added: "Shouldn't we also ask the question: at what cost to our own state education system?
"Are we in danger of overlooking one of the consequences of this expansion - a teacher 'brain drain' from this country just when the supply issue is reaching situation critical?
"At a time of well-documented shortages, should we not be putting more effort into holding on to those who have gone through their teacher training in England?"
And he called for policy makers to consider financial incentives, often referred to as "golden handcuffs", to retain teachers working in the UK state system.
Sir Michael also said there was a need to "talk up" the profession and highlight the "nobility of teaching" and how it can transform lives.
"The idea of 'golden handcuffs' to keep teachers in this country for a period of time is an interesting one which deserves more examination."
A Department for Education spokesman said: "Despite the challenge of a competitive jobs market, the proportion of trainee teachers with a top degree has grown faster than in the population as a whole, and there are more teachers overall.
"But we are determined to continue raising the status of the profession.
"That's why we're investing hundreds of millions in teacher recruitment, backing schemes like Teach First and the National Teaching Service to get great teachers where they are most needed, and why we've given schools unprecedented freedom over staff pay, to allow them to attract the brightest and the best.
"The number of former teachers returning to the classroom has increased year on year - further evidence of the popularity of the profession. Recent research shows that the number of teachers leaving the profession to work abroad is 1%."
This percentage is based on separate figures from research based on England's Labour Force Survey. Wales does not compile figures on teachers leaving the country.
By Hannah Richardson
A teacher training certificate in British education has always been a passport to rewarding work in interesting parts of the world.
What is worrying is that this alleged "brain drain" comes amid a growing teacher recruitment crisis in England.
Because of high staff turnover, the equivalent of an entire British Navy of teachers has to be recruited every year, just to stand still.
So financial incentives or "golden handcuffs", that might staunch the flow of those leaving may well tip the balance.
A scheme to attract and retain teachers in challenging schools began in 2009 but was axed in 2010.
Official "golden hellos" or cash bonus schemes, to attract teachers into shortage subjects and tough areas, were used by the Labour administration.
These were scrapped in 2011 and new bursary schemes giving trainee teachers money off their higher university tuition fees became the key incentive.
But teaching unions say, fee-waivers do little to address the low starting salary for teachers - £21,000 outside London - and the pressures of increasing workload and accountability.
Shadow education secretary Lucy Powell said: "Whilst ministers continue to deny the crisis in teacher shortages, we are seeing more and more evidence that this serious issue is threatening standards. Sir Michael Wilshaw is right to highlight the detrimental impact this is having on schools right across the country."
Leora Cruddas, director of policy at the Association of School and College Leaders, said: "Our view is that more needs to be done to incentivise teaching as a career.
"We would suggest that government undertakes to write off, over a period of time, the undergraduate tuition fees of students who become teachers, as long as they remain in the state system in this country during that period.
"This would help with both the recruitment and retention of newly qualified teachers."
Christine Blower, general secretary of the National Union of Teachers, said performance-related pay and an "utterly punishing" workload that leaves little time for family or friends is driving teachers out in droves.
"Add to this the punitive and often pointless accountability system overseen by Sir Michael Wilshaw alongside his regular disparaging comments about the profession, it is no surprise teaching in England has become an unattractive option."