The Foreign Office spends more than £14m per year on private school fees for children of its staff, including £6m for staff based in the UK.
The figures were revealed in a ministerial response to a parliamentary question by Liberal Democrats.
It meant that last year staff stationed in the UK received school fees worth on average more than £33,000 per year.
Lib Dem leader Tim Farron said: “That is a perk of the job that needs to be looked at seriously.”
A Foreign Office spokeswoman said diplomats who worked overseas who might have to travel at short notice had allowances for school fees so that their children could avoid having their education disrupted.
Foreign Office ministers were asked how much the department had spent on private school fees for the children of staff stationed either overseas or in the UK during 2015-16.
Call for review
The response, from Sir Alan Duncan, said that 179 diplomatic officers stationed in the UK were in receipt of school fees of £6,005,124.
For 173 diplomatic officers stationed overseas, school fees cost £6,403.938.
There was support paid for a further 1,108 children, said the answer, with the total annual cost of fees being £14,207,444.
Mr Farron said that paying so much on private and boarding costs, particularly for staff based in the UK, was “not acceptable”.
“Why can’t staff send their children to the good or outstanding local school?”
Mr Farron said the Foreign Office should review this spending – and if there was any spare cash it should be targeted at pupil premium support for disadvantaged pupils.
A Foreign Office spokeswoman said that “some members of the diplomatic service must be prepared to serve anywhere during their career, sometimes at very short notice”.
“In some parts of the world we do not permit staff to take their children with them for safety reasons, in others local schools of an acceptable standard are not available.
“In these cases it is longstanding practice that the Foreign and Commonwealth Office helps staff by providing support for their children’s education.”