Number 10 was unable to say when the first flights sending migrants on a one-way trip to the east African nation would take off, in the face of criticism and legal action against the plans.
But officials insisted it was not waiting for court challenges to be resolved before putting the policy into practice.
It comes as analysis of Government figures by the PA news agency shows 7,240 people have reached the UK after navigating busy shipping lanes from France in small boats since the start of 2022.
Crossings continued on Tuesday with young children among those being brought ashore.
Earlier this month, Home Secretary Priti Patel signed what she described as a “world-first” agreement with Rwanda, which will see it receive asylum seekers deemed by the UK to have arrived “illegally” and therefore inadmissible under new immigration rules. But the deal is already subject to legal challenges.
The Prime Minister’s official spokesman said the flights would take place at the “earliest opportunity” and the plan was a “fully legally secure approach that has been tested and thought through”, adding: “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.”
Refugee charities claim the Rwanda policy has done little to deter people from making the journey to the UK, with 1,972 people arriving between April 14 – when the Government announced and signed the Rwanda deal – and May 2.
More than 500 people arrived in Kent over two days this weekend after an 11-day stretch between April 20 and April 30 without any taking place amid bad weather conditions.
When asked if Mr Johnson was disappointed the plan was yet to curb crossing numbers, the spokesman said: “It’s too early to judge what the situation will be long-term on this policy.”
The total for this year so far is more than three times the number recorded for the same period in 2021 (2,390) and more than seven times the amount recorded at this point in 2020 (1,006).
Overall, 28,526 people made the crossing in 2021, compared with 8,466 in 2020, 1,843 in 2019 and 299 in 2018, official Home Office figures show.
Despite the increasing numbers, the UK’s small boat arrivals are a fraction of the number of people arriving in Europe.
Data from the UN’s refugee agency shows at least 120,441 people arrived in Europe via the Mediterranean by land and sea in 2021.
Steve Valdez-Symonds, Amnesty International UK’s refugee and migrant rights director, said: “Ministers have made the entirely reckless political calculation that they would rather be taken to court over their scandalous approach to refugees than put in place policies and practices that actually assist people fleeing conflict and persecution and diminish their vulnerability to exploitation and smugglers.”