They gave support and advice to 1,485 people last year but it is thought that many other cases go unreported.
The Unit is a joint initiative by the Foreign Office and the Home Office, who have permission to intervene when they believe a child under 18 is at risk of becoming a victim of forced marriage.
Figures they have released show that of the 250 children in these cases who were protected, 82% were female and 18% male. They were from 60 different countries – 47% involved Pakistan, 11% Bangladesh and 8% India.
There were 114 cases involving people with disabilities and 22 involving victims who described themselves as lesbian, gay, bisexual or transgender. 16 to 25-year-olds were most at risk of being forced into marriage, and the oldest victim was 71.
Carla Thomas, head of the unit, said that cases with very young victims were protecting them from being promised to future marriage.
Unlike arranged marriages in which those taking part give their consent, forced marriages may involve kidnapping as well as physical and mental abuse.
Within the UK, they help those at risk of becoming victims or who are already in that situation, and civil courts have the power to prevent weddings taking place by issuing Forced Marriage Protection orders.
They also work with embassy staff outside of the UK to rescue those who may have been taken out of the country, even if they are going to be entered into a forced marriage abroad.
Jeremy Browne, the Home Office minister, said the figures showed an alarming number of victims:
Forced marriage is a devastating form of abuse that is absolutely unacceptable in our society.
David Cameron has insisted forced marriage must be stamped out and has pledged legislation to make it a criminal offence in England and Wales as currently it is not illegal in Britain to make someone get married against their will.
It emerged last year that a 5 year old girl had been forced into a marriage and an 87-year-old woman was also a suspected victim in 2011.