The Mayor on Thursday wrote to Suella Braverman outlining his “strong opposition” to “unsafe and unworkable” proposals to moor refugee accommodation just a stone’s throw both from City Airport and his own offices.
But City Hall warned Mr Khan would not be able to block the scheme if the Government pressed ahead.
“Today I have written to the Home Secretary to outline my strong opposition to any proposals to use London as the location of barges to accommodate those seeking asylum in the UK,” Mr Khan said.
“We were recently approached by the Home Office asking to use the Royal Docks as a location for a barge. To be clear these plans would be unsafe and unworkable, and they risk the health and wellbeing of already highly vulnerable people.
“London has a proud history of providing sanctuary for those seeking refuge.”
London mayor Sadiq Khan has spoken out against the plans/ PA Wire
He accused the Government of fostering a “cruel and inhumane” approach to asylum seekers.
“Ministers need to completely rethink their plans as a matter of urgency,” he added.
The Home Office approached the Royal Docks Management Authority (RoDMA) some weeks ago about the possibility of mooring a barge for asylum seekers in the east London docks.
Newham Council and the Metropolitan Police are understood to be opposed to the proposition on safety grounds.
RoDMA is also expected to confirm its formal objection in the coming weeks.
However, the Mayor does not have veto powers over the area and the Home Office could press ahead if the Government passed primary legislation.
Newham councillor Dr Rohit Dasgupta said: “We are completely opposed to this plan. Newham is a borough of sanctuary and we will not allow the UK government [to] play their politics of hate here.”
Prime Minister Rishi Sunak confirmed on Monday that the Government had acquired two giant barges to house about 1,000 people seeking refuge in the UK.
Their locations have not yet been confirmed, but Liverpool and Middlesborough are understood to be under consideration.
A third barge will be moored off the coast of Dorset.
A Home Office spokesman refused to comment on the Royal Docks, but said: “The pressure on the asylum system has continued to grow and requires us to look at a range of accommodation options which offer better value for the British taxpayer than expensive hotels.
“We understand the concerns of local communities and will work closely with councils and key partners to manage the impact of using these sites.”
It comes as the Government pressing ahead with parliamentary scrutiny of it controversial small boats legislation into the early hours of the morning was branded “disgraceful”.
A detailed debate on the Illegal Migration Bill continued until after 4am this morning in the House of Lords.
Critics argued it was “disappointing” that matters, including the care of unaccompanied migrant children and detention of pregnant women, were being dealt with in such a way.
The proceedings of the upper chamber, which started at 3pm on Wednesday were eventually adjourned shortly before dawn at 4.16am.
Labour former minister Lord Bach said: “Can I for my own part say how disgraceful I think it is we are debating these really important and serious matters at this hour in the morning.”