Whatever your views on immigration surely noone can approve of a force which so misuses power sometimes with no legal backing whatsoever. Immigration Enforcement have been found to have:
Racial bias. Workplace raids are massively skewed towards certain ethnic groups; people from India, Pakistan and Bangladesh account for 75% of all those arrested.
"Low grade" intelligence. While claiming to be "intelligence led", the majority of operations are based on "low grade" tip-offs from "members of the public", classified as "uncorroborated" information from "untested sources" in the official intelligence rating system.
Entry without warrants. In the majority of raids, Immigration Enforcement teams do not in fact have court-issued warrants. A sample carried out by the Independent Chief Inspector of Borders and Immigration in December 2015 found that teams had warrants in only 43% of cases. In many other raids, Immigration Officers claimed they had "informed consent" to enter premises. But the Inspector noted numerous irregularities in Immigration Officers' understanding of "consent", and that there was no record keeping to actually demonstrate whether or how consent had been given.
Independent Chief Inspector's criticisms. An earlier 2014 report by the Independent Chief Inspector of Borders and Immigration strongly criticised Immigration Enforcement for entering premises without warrants, including doing so unlawfully, and widely abusing the system of "Assistant Directors' Letters" to enter without due legal process.
Abuse of "consensual questioning". The Independent Chief Inspector found that, contrary to legal guidance, raid teams routinely round up and interrogate everyone in a premises, whether or not they are a named suspect. They are only supposed to ask "consensual questions" of people who are not named suspects. However, according to the Inspector, “In the 184 files we sampled there was no record of anyone being ‘invited’ to answer ‘consensual questions’. The files showed that officers typically gathered everyone on the premises together, regardless of the information known or people's actions.”
Not exactly a great record of fair treatment.