Suella Braverman has questioned the productivity of civil servants who process asylum claims, and declined to rule out using cruise ships to house people seeking refuge in the UK, after admitting that the cost of providing accommodation for claimants will rise to £3.5bn this year. The home secretary told peers on Wednesday that the productivity of her department’s staff had been “too low”, resulting in caseworkers processing one case a week on average. Braverman also confirmed reports that the Home Office is looking at ideas for using alternative accommodation other than hotels to house people seeking asylum, and she suggested officials were in talks with ship companies. She has been accused of failing to ensure that there was been enough hotel accommodation to house asylum seekers this autumn which resulted in illegal detention at Manston processing centre last month. Braverman has denied being responsible for a lack of accommodation. Appearing before the House of Lords justice and home affairs committee, she said: “There is a large amount of transformation that we want to embark upon when it comes to asylum caseworking. “I should say just for context, what I have found during my few months here at the Home Office is that we have very different practices. Our asylum caseworking team do a great job but their productivity, frankly, is too low. The average decision-making rate of a decision-maker per week is one. We need to increase that considerably.” The government had doubled the number of caseworkers, Braverman claimed, and officials had been trialling a more rapid system that she hoped would mean that the number of cases covered by a single caseworker would treble. Addressing the problem of housing asylum seekers in hotels – an issue that has angered backbench Conservative MPs – she confirmed that her office was looking at alternative accommodation, including cruise ships. “You then asked about cruise ships. We want to end the use of hotels as quickly as possible because it’s an unacceptable cost to the taxpayer, it’s over £5m a day on hotel use alone,” she said. “We will bring forward a range of alternative sites. They will include disused holiday parks, former student halls. I should say we are looking at those sites, I wouldn’t say anything is confirmed yet,” she said. The Liberal Democrats’ home affairs spokesperson, Alistair Carmichael, said Braverman was doubling down with the same failed approach as other recent home secretaries. “Her ludicrous proposals to house refugees in cruise ships will once again be ineffective and incredibly expensive,” he said. Braverman confirmed reports that she plans to change anti-slavery laws because of concerns that they are being abused by a minority of asylum claimants. However, neither she nor Matthew Rycroft, the Home Office permanent secretary, could explain why there was no anti-slavery commissioner in place to scrutinise any new laws, despite a legal requirement to have someone in post. The last commissioner, Dame Sara Thornton, left the job in April. Rycroft said he would write to the committee with an explanation. Braverman confirmed that the government would spend £3.5bn on accommodation and support for asylum seekers and refugees in 2022-23, including £2.3bn on hotels. At present, 57,000 people are housed by local authorities under the asylum dispersal scheme – a figure she said she wanted to increase to 100,000. Braverman was questioned by the Labour peer Shami Chakrabarti about reports that civil servants have admitted in leaked emails that hundreds of people were illegally detained at immigration removal centres in November. The detention centres were used to hold about 450 people, described in one email as “overflow” from the processing facility at Manston. One email from 4 November obtained by the BBC said their detention was “no longer legal”, adding: “We need to move them to hotels ASAP.” Braverman said thousands of people had arrived in the UK via small boats in October and there were not enough beds in suitable accommodation. “The reality of those several weeks was that outflow was being exceeded by the inflow because it was very difficult to procure sufficient numbers of beds from across the country. It was a very challenging situation,” she said.