African countries are planning to force Britain to hand over slavery reparation in a Chagos-style legal battle.Members of the African Union are planning to haul their former colonial powers into international courts to argue the transatlantic slave trade comprised a crime against humanity.Legal advisers working with the African Union (AU) believe the legal argument which led to the Chagos “surrender” deal with Mauritius could be used to force Europe’s hand over reparations.The International Court of Justice (ICJ) issued an advisory opinion that Britain was “under an obligation” to end its administration of the Chagos Islands, which led to the agreed £30billion transfer of the British Overseas Territory.One source told The Telegraph the Chagos case had been successful in establish the argument for reparations, and the continent appreciated Britain’s commitment to international law.They added: “If you accept that level [the Chagos opinion], then what international law says about recognising the transatlantic slave trade as a crime against humanity must also be recognised.”Campaigners have claimed reparations packages could be worth trillions of pounds.In practice, these reparations could come in the form of debt relief, official apologies, development funding, or economic relationships.The African Union comprises 55 member states across the continent and meets in Addis Ababa, Ethiopia | GETTYThe campaign is aimed at European powers which engaged in the transatlantic trade slave, including Spain, Portugal, France, and Britain.Two expert committees have been organised by the AU to develop “innovative legal and diplomatic strategies” to gain reparations.A legal strategy on the table involves using UN mechanisms and “advisory opinions” from the ICJ to shift “global norms and practices” towards a legal case for reparations.Amr Aljowaily, a senior AU official, confirmed multiple strategies were being developed to push the case for reparations through international law.The African Union will produce a ‘common African position’ on reparations | GETTYAnother approach frames reparations as an attempt to address “economic disparities between Africa and the Global North”.This strategy suggests that in the context of climate change, developed countries within the “Global North” would need to compensate Africa for their “historical responsibility for environmental degradation”.The AU, which comprises 55 member states, plans to produce a “common African position” which sets out the types of reparations sought.The UN General Assembly sought an opinion on Chagos in 2017 and more than half of the votes came from AU nations.Britain was deemed to be “under an obligation” to end its administration in Chagos when the UN international tribunal for the law of the sea supported a decision by the ICJ.John Mahama, the President of Ghana, will table a UN resolution to declare the transatlantic slave trade a crime against humanity | GETTYMartin Okumu Masiga, an AU legal adviser, said there was a clear legal precedent for compensation for historical crimes.He cited Germany paying reparations for the Holocaust, the US compensating Japanese-Americans placed in internment camps during the Second World War, and the UK’s compensation to victims of human rights violations in Kenya as examples which proved reparations to be “possible”.Lord Hermer, the Government’s chief legal adviser, was a member of the legal team that secured compensation payments to Kenyans in 2013.Earlier this month, Labour backbencher Bell Ribeiro-Addy voiced support for Britain to spend billions of pounds in “colonial reparations”.Justice Secretary David Lammy has previously voiced support for reparations, saying it could take the form of “non-financial reparatory justice”.A UN resolution to declare the transatlantic slave trade a crime against humanity will be tabled by Ghana in two weeks and is considered the first step to reparations.