The home secretary has announced that the UK Border Agency (UKBA) is to be abolished, because "its performance was not good enough".
Speaking to the House of Commons, Ms May told MPs that the agency, which was formed in 2008, will be broken down and its work returned to the Home Office. She explained that this return to Home Office control and the removal of agency status is necessary in order to tackle the "secretive culture" that has evolved in the UKBA.
Responsibilities will be divided into two parts, one of which will focus on the UK visa system for international talent and foreign visitors, while the other will tackle UK immigration law enforcement. However, both departments will report directly to ministers in an attempt to avoid the recurrence of the current issues with hidden errors.
Last year, the home secretary announced that the UK Border Force was to be separated from the UKBA to become its own separate law-enforcement body, but this week's announcement confirms further progress in this area.
In announcing the changes, Ms May said: "The performance of what remains of UKBA is still not good enough. The agency struggles with the volume of its casework, which has led to historical backlogs running into the hundreds of thousands.
"The number of illegal immigrants removed does not keep up with the number of people who are here illegally. And while the visa operation is internationally competitive, it could and should get better still."
She added that dividing the body will create a "high-volume service that makes high-quality decisions about who comes here", explaining that the second section of the agency will become an organisation with "law enforcement at its heart".
The announcement comes after a Home Affairs Committee report stated earlier this month that the border agency is "not fit for purpose", with particular reference to its problems in addressing the backlog of asylum cases in Britain.