A vital border security system is failing to check the passports of every person arriving in Britain against terrorist and criminal watchlists, a damning report reveals today.
As the UK fights to stop extremists sneaking past their porous borders, the Home Office admitted it did not know how many people were entering the country "unchecked".
The department is supposed to check 100 per cent of foreigners' passports against security databases before they travel under the controversial eBorders programme and its successor.
But a series of catastrophic IT failures and management blunders means the UK currently collects advanced passport data from only 86 per cent of the 118 million people travelling here each year, according to the report by MPs.
It means 17 million people - about one in seven - are not screened before their arrival, denying officials full use of a crucial weapon in the fight against terrorists, sex offenders and human traffickers trying to sneak into Britain.
The withering report from the Commons' Public Accounts Committee (PAC) says the gaps exist despite the Home Office squandering £830 million on the failed eBorders scheme - axed in 2010 - and its replacement, the Digital Services at the Border programme.
Incredibly, this may not be in place until 2019 - eight years behind schedule - and another £275 million is expected to be spent on it before then, taking the total to more than £1.1 billion.
Critics warned the "worrying complacency" over our crisis-hit border system risks gravely undermining Britain's national security.
The report also reveals that passport checks are not carried out on everyone who arrives in the UK in private planes and ships at small airfields, harbours and marinas - leaving Britain vulnerable to criminals arriving here unhindered. Dismissing Government assertions that 100 per cent of passports were checked as "both imprecise and unrealistic", the PAC report said: "These numbers do not take any account of those that enter the country via land from the Republic of Ireland, or full account of those that travel via smaller craft known as general aviation or general maritime.
"The department told us that [it] makes a risk-based decision on whether to check passports or not."
It added: "The department does not estimate the percentage of unchecked passports to determine what risks these pose nor does it adequately measure the quality of the data it holds on individuals travelling to the UK and on those of interest to the UK government."
Meg Hillier, Labour chairman of the PAC, said: "If you collect information before people arrive the more chance you have to stop them entering the country in the first place.
"Successful completion of this project is essential to the security of our international borders. Yet the original target date has long passed and we are still at least three years away from delivery."