Plans to remove foreign criminals and illegal immigrants were cancelled in 40% of cases, an independent report has found.
Close to 34,000 plane tickets had to be cancelled in 18 months, according to a report from the Independent Chief Inspector of Borders and Immigration.
A lack of security staff to accompany detainees out of the country was a "major constraint", the report said.
The Home Office has outsourced some of its border and immigration functions to private contractors and the report, covering July-November 2015, examined the escorted and non-escorted removal services provided by private firms.
It found that the Home Office and the companies contracted for the removal services were slow to resolve issues and reach agreement on areas for improvement.
The recorded loss on unused tickets was £1.4m - equivalent to 4% of the total amount spent on tickets - although records were not always kept, inspectors found.
Home Office figures for October 2014-March 2015 showed that on average 2.5 tickets were issued for each individual successfully removed.
In the financial year 2014-15, "40% of all planned removals were cancelled".
As enforced removal is resorted to only when someone will not leave voluntarily, efforts to delay or stop deportation, through legal challenges or non-compliance, are commonplace.
The report said: "The Home Office regarded some of the reasons for failed removals to be 'out of (its) control'.
"While this might be true in individual cases at the point of removal, it was unclear what steps were being taken to identify lessons that might be applied by the Home Office and others to reduce 'out of control' failures."
The Home Office accepted the report's recommendations and said it was look for ways to reduce the cost of pre-departure accommodation at a unit for families subject to enforced removal.
An official response said: "Work is already under way to address the recommendations relating to ticketing and escorting and, as the report acknowledges, these issues are being factored into the re-procurement exercise for both contracts which began in 2015."