Boris Johnson's plan to send asylum seekers to Rwanda is already being hit by delays as No10 admitted it could be "months" before the first flights leave.
The Prime Minister announced the controversial scheme last month, in an attempt to curb rising numbers of people making the perilous Channel crossing in small boats.
Under the five-year deal with Rwanda, people deemed to have travelled to the UK illegally would be flown 4,000 miles to the central African state for processing.
Critics have warned the cruel scheme will not solve the problems it claims to tackle and could rack up extortionate costs.
The Government was widely reported to want the first flights to begin at the end of May but the PM said the plan could be held up by legal challenges.
Downing Street admitted today that it could be months before any asylum seekers are sent on a one-way trip to Rwanda, partly due to legal wrangles.
More than 7,000 asylum seekers have arrived in the UK after crossing the English Channel this year so far, according to analysis of government data.
Some 1,972 people arrived in the UK after crossing the Channel between April 14 - when the Government announced and signed the Rwanda deal - and May 2.
Asked if Boris Johnson was disappointed that the plan had not curbed Channel crossings, his official spokesman said: "It's too early to judge what the situation will be long-term on this policy.
"You will know - as we've seen - migrant crossings continue, criminal gangs continue to profit. This is unsustainable."
Asked when the success or failure of the plan could be judged, the PM's spokesman said: "I don't think there's a fixed date ... obviously, there are a number of variables we need to deal with, not least some of the legal challenges which have been talked about."
The spokesman was unable to say when the first flight would be.
He said: "We have received pre-action correspondence from a number of legal firms, I can't get into that more ... but we still maintain our hope to have the first flights take place in a matter of months."
The Government managed to ram the Nationality and Borders Bill through Parliament last week, in a series of late night clashes in the Lords ahead of prorogation.
The bill makes it a criminal offence to knowingly arrive in the UK illegally and includes powers to process asylum seekers overseas.
