The death toll in Kenya exceeds that from floods triggered by the El Nino weather phenomenon in late 2023.
The Ugandan parliament urged Britain to respect the country's sovereignty.
The remains were retrieved from mass graves in Ngoma village following a tip-off from a construction worker in October last year.
More than 7,500 migrants have arrived in England on small boats from France so far this year.
Kenyan authorities have reported that at least 169 people have died due to flooding, with about 200,000 individuals displaced across the nation.