Schools are having to conduct mass recruitment rounds abroad as new figures show a record 50,000 teachers have left the profession in a year.

An exodus from schools, along with a shortfall in applicants for teacher training, has left heads unable to fill key positions. They are instead being forced to scour the globe, with academy trusts recruiting up to 50 teachers in single whistlestop visits to Jamaica and elsewhere.

The government has also started encouraging foreign teachers to consider moving to England, with officials “building relationships with target countries”, according to a letter seen by the Observer.

The letter, sent to a recruitment agency by a Department for Education official, adds that ministers plan to “help widen the existing recruitment pool by supporting schools to confidently recruit where necessary internationally”.

An appeal on the department’s website boasts to foreign teachers of generous starting salaries, adding: “Have you considered progressing your teaching career in England? As a talented, qualified teacher, you are in demand. Making the move to England is a great way to gain experience at the start of your career and build your résumé.”

Shadow education secretary Lucy Powell claimed the crisis in teacher numbers was due to a combination of a botched handling of recruitment, a lack of forward planning and the denigration of the profession by former education secretary Michael Gove.

Between November 2013 and November 2014, 49,120 teachers left the profession – an increase of 3,480 teachers on the previous year, and the largest number to quit in a year since records began.

Applications to teach are also down – by 21,000 compared with this time last year. The DfE claims that this is in part due to Scottish recruitment no longer being included in the figures, but the numbers are falling in every region.

Meanwhile, pupil numbers continue to grow – with a projected 582,000 more primary and secondary-age pupils by 2020 – requiring thousands more teachers just to maintain class sizes at their current level. The country will need nearly 160,000 additional teachers over the next three years, yet on current trends there could be a shortfall of 65,000 applicants over this period, Labour claims.

‘Headteachers have had a considerable challenge recruiting maths, English and science teachers’ Joan McVittie, London head

Powell, who was appointed shadow education secretary by Labour leader Jeremy Corbyn last month, said: “I don’t blame schools for looking abroad. For years, this government chose to ignore the growing problem with teacher supply, continuing instead to botch recruitment and do down the profession at every opportunity.

“As a result, schools are now struggling against falling applications and the highest number of teachers quitting the profession on record. The Tories’ failure to take this problem seriously is threatening standards in our schools and damaging the education of our children – it cannot go on.”

A Conservative spokesman insisted that Powell was scaremongering and said progress was being made in recruitment for secondary schools, while targets were being exceeded in the primary sector. He said: “Far from the picture painted by the Labour party, teaching remains a hugely popular profession, with 3% more people due to start postgraduate teacher training than this time last year.

“The latest figures show the number of former teachers coming back to the classroom has continued to rise year after year. There are now 13,100 more full-time equivalent teachers than in 2010.”

However, Dame Joan McVittie, head of Woodside high school in Haringey, north London, claimed ministers were ignoring the problem.

“Last summer, there was a considerable challenge among my headteacher colleagues in recruiting maths, English and science teachers,” she said. “If we want specialist teachers, we will have to ask our specialists to teach double classes or use technology to relay lessons to other classrooms.

She added: “By ignoring the problem at government level for so long, even if there was a solution tomorrow it will be two to three years before these new teachers are in the classroom. Sadly the children will suffer.”