The details of 600,000 foreign visitors have slipped through the cracks of the Home Office's database thanks to its "shambolic" exit checks system.

A report (PDF) by the chief inspector of borders and immigration, David Bolt, examined the department's Initial Status Analysis (ISA) system database and how ISA-produced data had been used by the Home Office and other agencies.

It found that as of 31 March 2017, there were no departure records of 88,134 non-EU visa nationals with ISA "identities" – whose visas typically last six months – nor for 513,088 identified non-visa nationals.

Staff told the inspector they lacked confidence in the system, which they said had been "mis-sold", while an airline official described it as "shambolic".

Bolt said: "Overall, the sense was that the Home Office had overpromised when setting out its plans for exit checks, and then closed the exit check programme prematurely, declaring exit checks to be 'business as usual' when a significant amount of work remained to be done to get full value from them."

Since 2004, as part of the troubled "e-Borders Programme" (currently running eight years late at a cost of £1bn) 16 airlines have been required to share advanced passenger information with the Home Office.

Carriers transmit API data via an encrypted link to the Home Office, where it is received into Semaphore, an IT system created to test the e-Borders concept in advance of the intended procurement of the main e-Borders system.

Between April 2014 and April 2015, as part of the Exit Checks Programme, the Home Office developed the ISA database, which matches inbound and outbound travel data received via Semaphore with data recorded on its other immigration related systems.

Between April 2015 and March 2017, the Home Office received over 607 million UK data records relating to outbound travel. But somehow it lost track of the details of 600,000 foreign visitors.

The Home Office said that a lack of evidence of departure was not confirmation that an individual remained in the country, only that they had not been matched to a departure record.

However, it does not bode well for the further challenges facing the department after Brexit.

The Public Accounts Committee has already warned that the border could be left exposed after Brexit because departments have failed to plan for new IT systems.

Around 30 of the 85 IT systems used at the border will need to be replaced or updated in some way. This includes requirements for five entirely new systems and three replacements, along with systems provided by the EU. ®