I think a lot of people confuse "Legal immigration" with "illegal immigration".
Quite rightly, those people who qualify to enter into the UK legally under the immigration rules should be allowed to do so and it is irrelevant what nationality, skin colour, ethnic origin etc they are - they are a benefit to the UK, because they bring skilled labour, pay taxes and contribute to a multi-cultural society.
Illegal immigrants are often economic migrants, who are looking for a better life than the one in their home country. Because they do not qualify for legal entry under the immigration rules, they resort to entering the UK clandestinely, and then either work illegally or claim asylum.
If they claim asylum, then under the terms of the 1951 Geneva convention, the UK has to consider their asylum claim. They have the right to help whilst this is going on - certain benefits, legal aid, etc. There is no question that this is often abused and economic migrants claim to be someone who requires political asylum. Their application is quite rightly refused by the UKBA (because they are not a genuine applicant) and they become a failed asylum seeker, who often still remains a drain on UK resources because they appeal against removal, etc.
Regardless of the rights or wrongs of illegal entry into the UK, the illegals/asylum seekers still have to be treated as basic human beings and given rights because we are a civilised society. "They are not bringing Britain to its knees" - successive morons in government are doing that.
The UKIP is a racist party feeding on the fears of the daily mail reading masses. Immigrants will not "destroy" Britain. And I say that as an ex-immigration officer who worked at the sharp end in enforcement for over 10 years.