Labour and unions have alleged staff shortages, following cuts to the UKBA, are behind relaxation of border controls in the summer.
The assertion comes at a time when some 5,000 posts are due to go by 2015 as part of wider government cost-saving measures.
The assertion is significant as Home Secretary Theresa May is expected to make a statement before the Parliament. It follows the action to place under suspension three UK Border Agency officials over claims that the border controls were relaxed in the summer.
Among the three is Brodie Clark, head of the UK border force and a board member of the UK Border Agency (UKBA).
The allegations are that staff were told to relax identity checks on non-EU nationals.
May has ordered an independent inquiry into the allegations.
The official investigation into the claims will be led by the Chief Inspector of the UK Border Agency, John Vine.
Already, Labour have demanded details whether anyone posing a risk to national security was allowed to enter the UK during that period.
It was in July that the Home Office said checks on EU nationals could be reduced in "limited circumstances". It was added their biometric passports could be checked "upon the discretion of a UKBA official" instead of automatically.
It is now being alleged that Clark, on the other hand, told the staff not to carry out checks on the biometric passports or fingerprints of thousands of people from outside the EU. The allegations are that he also told the staff to relax checks against watch lists, which are aimed at flagging up people "of interest" to border staff.
Shadow home secretary Yvette Cooper has, meanwhile, shot off a communication to May seeking details of how many terror suspects or illegal immigrants could possibly have entered during the period covered by the claims.
Cooper said it was imperative to ensure the independent inquiry had a wide-enough remit to fully investigate "the actions of the Home Office, ministers and the effect of resource cuts on UKBA decision-making".
Also, the Home Office and UKBA should publish all documents and correspondence relating to the issue of passport checks.
Cooper added the inquiry must also examine why it took four months for the ministers to be informed about reports that passport procedures were being ignored.
The BBC quoted Lucy Moreton, from the Immigration Services Union, as saying: "Every passenger coming into the UK is supposed to be seen by an immigration officer, but there are instances where there are not enough staff and where, in fact, entire aircraft are missed, particularly flights that come into small, what we would call non-approved, airports.
"We have a very large coastline… freight traffic coming into some of the large seaports can be missed.
"It's not supposed to happen, and often it doesn't happen on purpose, but it does happen."