Only a third of immigration arrests following tip-offs from the public resulted in deportations last year, official figures show.
Immigration Minister James Brokenshire revealed that of the 4,535 arrests made for immigration offences in 2013 after allegations made by members of the public, only 1,585 people were removed from Britain.
Only 15 criminal prosecutions were started in relation to the arrests.
Mr Brokenshire released the figures in response to a written parliamentary question from shadow immigration minister David Hanson.
Mr Hanson said: "These figures show that the Government just can't get a grip on illegal immigration. Only a third of people arrested last year after public tip-offs were being deported, a shocking record and one that the Government should be ashamed of.
"For people to have confidence in our borders and immigration system, it's crucial that people who are here illegally are found and deported from this country.
"Public reporting is vital in helping tackle illegal immigration, and Theresa May's department has to start taking simple steps to ensure these arrests are properly investigated and people who are here illegally are removed."
The Home Office said there was insufficient evidence to progress a third of all cases regarding suspected illegal immigrants reported by the public.
A Home Office spokesman said: "The immigration system we inherited was shambolic and open to abuse. We are building a system that is fair to British citizens and legitimate migrants and tough on those who abuse the system and flout the law.
"We take all reports of illegal immigrants in the UK seriously, but not all the information we receive is accurate. When tip-offs do lead to arrests, there are many legal barriers that can prevent speedy deportation.
"We are addressing several of these barriers through the Immigration Bill. It will cut the number of appeal rights from 17 to four, allow us to return people while their appeals are ongoing and ensure that judges deal with Article 8 claims in the right way - making clear the right to a family life is not regarded as absolute and unqualified."