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.
Last year more people left to teach abroad (18,000) than trained (17,000) on 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 Wilshaw'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 over 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 climates".
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%."