My personal guess about these dealys are that they might be linked to the arrival of the 'P1' variant of Sars-CoV2 in to the UK. It transpires that two people did not complete their docuements and were not fully checked on arrival. They are now: BBC:
The search for an individual infected with the Covid variant first found in Brazil has narrowed to 379 households in south-east England, Health Secretary Matt Hancock has said.
So, once again, they have proved that after a vote to secure the border taken enthusiastically on board by the Tory party 4.5 years ago - they have failed to do so.