Civil servants have threatened ministers with legal action over concerns that senior Home Office staff could be in breach of international law if they implement the government’s Rwanda deportation bill. The FDA union, which represents senior civil servants, have warned they could also be in violation of the civil service code – and open to possible prosecution – if they followed a minister’s demands to ignore an urgent injunction from Strasbourg banning a deportation. It has sent a pre-action legal letter to James Cleverly, the home secretary, calling for clarity – with a request to either amend the legislation or change the code. The safety of Rwanda (asylum and immigration) bill states that it is for ministers to decide whether to comply with decisions by the European court of human rights to temporarily halt a deportation. “The concern of the FDA and many of its members is that if ministers instruct civil servants not to comply with an interim measures indication, they will be putting the UK in breach of international law,” the letter said. With the bill due to return to the Commons next week, and the government expected to try to get the first flights off the ground within days of that, the FDA warned that it “may require legal proceedings” to clarify the matter. People who have been refused asylum could reportedly be offered thousands of pounds to move to Rwanda under a new voluntary scheme. The proposals, which are separate from the main scheme and are understood to have been agreed with Kigali, are designed to remove people who have no legal right to stay in the UK but cannot be returned to their home country, according to the Times. It will be aimed at individuals who do not have an outstanding asylum claim and are in a position to be relocated swiftly. An intervention by a Strasbourg judge last June stopped the only attempted deportation flight from taking off for Rwanda. Dave Penman, the FDA’s general secretary, said in his letter that the government had acknowledged there was a problem and planned to issue draft guidance to make it clear that it was the responsibility of civil servants to implement the decisions of ministers. Sir Matthew Rycroft, the Home Office’s top civil servant, said in a letter dated 17 January: “Given the nature of removal flights, officials should be available to advise ministers at short notice and during evenings and weekends. Home Office officials shall proceed with removal if the relevant minister approves that course of action.” But Penman said that while the FDA welcomed the government’s recognition of the need to clarify civil servants’ responsibilities, it did not consider the guidance to be adequate. He cited advice from the attorney general, revealed last month, that it was “beyond doubt” that interim measures from the court to stop a deportation were binding for the UK under international law and that there was “no respectable argument” to the contrary. The letter goes on to say that “difficulty arises because civil servants have personal legal obligations under domestic law not to act contrary to international law. That obligation is not capable of being over-written by any ministerial instruction or guidance.” The civil service code states that officials “must comply with the law”, which the government has previously confirmed includes international law, meaning that any ministerial instruction to ignore a Strasbourg ruling would be a breach of their terms of service. “Ministers do not employ civil servants and cannot unilaterally change or alter their terms of service,” the letter adds. “The guidance is erroneous in law and gives serious uncertainty for civil servants, and would foreseeably place them in an exceptionally difficult position”. The FDA warned that given the implementation of the new Rwanda bill in coming weeks, its letter was acting as a “pre-action notification of a potential claim for judicial review”, in the event of ministers instructing officials to ignore a Strasbourg injunction. A government spokesperson said: “Matters of international law are rightly a matter for ministers. In the event that the minister decides, in the light of full policy, operational and legal advice, not to comply with a rule 39 indication in an individual case, it is the responsibility of civil servants – operating under the civil service code – to implement that decision.”