UK ministers have acknowledged for the first time that they are detaining asylum seekers to be removed to Rwanda, prompting demonstrations outside Home Office buildings. Nationwide operations began this week to detain adult men and women, with more activity due to be carried out over the next 11 weeks leading up to a one-way flight to east Africa. Officials refused to say how many people had been held so far, but sources said there had been “dozens” of detentions across the UK, in cities including Glasgow, Liverpool, Birmingham and Bristol. Enforcement action is said to have taken place in England, Wales, Scotland and Northern Ireland. In a further development, the senior civil servants’ union has submitted an application for a judicial review against the government’s Rwanda plan. The FDA has said its members could be in violation of the civil service code if they follow a minister’s demands to ignore an urgent injunction from Strasbourg banning a deportation. The Guardian disclosed on Sunday that detentions would begin on Monday. Several asylum seekers who turned up for routine Home Office appointments on Monday were detained and told that they would be sent to Rwanda. The timing of the announcement on the Rwanda scheme, which is estimated to be costing more than £500m over five years, has prompted scorn from Labour. A party source said: “Is there any more blatant sign that [former immigration minister Robert] Jenrick was right about this all being symbolic before an election than this mad flurry of stories?” Downing Street denied this. The prime minister’s press secretary said: “From our part there isn’t really a day to lose when people are dying in the Channel having been induced into boats by gangs.” Demonstrations against the removals are taking place across the country, including outside immigration reporting centres in Liverpool, Hounslow in west London, and at the east Midlands immigration office in Loughborough. A demonstration was taking place on Wednesday outside Lunar House in Croydon, south London, where a Sudanese man was detained on Monday and told he was being sent to Rwanda. It is understood he has been taken to an immigration removal centre along with two other detained men. In a statement, the Home Office said the action was a key part of the plan to deliver flights in the next nine to 11 weeks. James Cleverly, the home secretary, said: “Our dedicated enforcement teams are working at pace to swiftly detain those who have no right to be here so we can get flights off the ground. This is a complex piece of work, but we remain absolutely committed to operationalising the policy, to stop the boats and break the business model of people-smuggling gangs.” The Home Office, which also released photographs and video footage of asylum seekers being detained in raids conducted by immigration enforcement officers, has been criticised for whipping up anti-asylum sentiments. Sacha Deshmukh, Amnesty International UK’s chief executive, said: “By drip-feeding updates about ‘round-ups’ and ‘detentions’ the government is callously seeking to exploit the predicament of people – many already suffering severe trauma from past persecution and abuse in countries they’ve fled and on journeys they’ve made.” Asylum seekers can only be detained if there is a realistic prospect of their removal from the UK. This means they could be released on bail in future if no action is being taken to deport them. The Home Office may have to refer them for a bail hearing if they have been detained for four months or more. Enver Solomon, the chief executive of the Refugee Council, said: “The government’s move to detain people is causing fear, distress and great anxiety among men, women and children who have fled war and persecution to reach safety in the UK. Children have been sending messages to our staff terrified that their age-disputed status will put them at risk of removal to Rwanda. We have also seen a worsening in the mental health and wellbeing of people we work with in the asylum system.” Labour has denied it will continue with the Rwanda removals in government, after a senior source told the New Statesman the party could retain the scheme while it tries to agree a returns agreement with the EU. Keir Starmer’s spokesperson said Labour would categorically not send any asylum seekers to Rwanda – though he said the party would not seek to bring back any people who were sent there under the Tory government. “The Labour government is not going to be scheduling any flights to Rwanda. We have said we want to ensure we have a proper returns agreement with other countries.”