Forcing travellers to the UK to stay in Covid quarantine hotels cost taxpayers about £400m, according to the National Audit Office.
Although the scheme was meant to be self-financing, about half the £757m cost has ended up being met by the taxpayer.
The National Audit Office has indicated that, in some cases, there were instances of profiteering, as well as £100m of unpaid room bills and fraud.
Ministers have admitted that they do not know if the system prevented the spread of dangerous variants of the virus.
A system of compulsory quarantine in hotels was introduced in January last year for travellers from countries thought to pose the highest risk of dangerous Covid variants.
Under the scheme 214,000 people stayed in such hotels, which cost £367 per family per night.
