Civil Liberties are liberties (freedoms, rights) given to citizens of a nation in the constitution or law of that nation. Examples are the right to own property and the right to work. Civil liberties are sometimes knows as civil rights, particularly in the USA (Hence Civil Rights Movement).

Due to the nature of the British constitution (Uncodified, 'flexible', 'evolutionary') British citizens traditionally do not have a list of their liberties. Rather, our liberties are what is left after all Acts of Parliament have been applied. Judges in the UK must judge within every Act of Parliament (Because and Hence we have Parliamentary Sovereignty.) Citizens of the USA have their rights defined in the Bill of Rights and Judges of the Supreme court can deem any legislation or practice to be unconstitutional if it breaches these.
To be precise, in 2000 The European Convention on Human Rights became UK law, and so we have a kind of Bill of Rights in the form of the 'Human Rights Act'. This is still only a run-of-the-mill statute law (and not entrenched), but there are procedures for judges to bring to attention any of the UK's current laws that are illegal under it.

Some cases concerning civil liberties in the UK:

The only way that there can be protection of British citizen's civil liberties is if there is sufficient scrutiny of and pressure on proposed legislation and executive action. As you can see, none of the Conservative Administrations of 1979 - 1997 had any regard for these liberties: Between 1979 and 1986 Margaret Thatcher prosecuted 29 people under the Official Secrets Act.