1. Human Rights Act
The Human Rights Act 1998 incorporated the European Convention on Human Rights into UK law and became effective on 2 October 2000.
While it's had its fair share of detractors, particularly in the Conservative Party, the Act has undeniably benefited a large number of vulnerable people.
2. House of Lords reform
The House of Lords Act, which removed the right of several hundred hereditary peers to sit in Parliament's upper chamber, became effective in November 1999.
Lords reform remained a thorny issue throughout the decade, however, particularly after the Commons voted for an all-elected second chamber in 2007 - which the Lords promptly ignored by voting for an all-appointed chamber.
Liberal Democrat Tom McNally said:
"The Lords' votes flies in the face of public opinion and commitments made by all three major parties at the last general election.
"A veto on constitutional reform by the Lords is unacceptable. It's now up to the Commons to assert its primacy."
But as we all know the Commons failed to do so. It will now fall on the next Government to decide how to proceed with reform.
3. New Supreme Court
Its creation was a landmark moment in British constitutional and legal development.
As President of the Supreme Court Lord Phillips of Worth Matravers said:
"For the first time, we have a clear separation of powers between the legislature, the judiciary, and the executive in the United Kingdom.
"This is important. It emphasises the independence of the judiciary, clearly separating those who make the law from those who administer it.
"And as Justices of the Supreme Court we will be more visible to the public than we ever were when sitting as members of the House of Lords.
"This is desirable as the Court will only decide points of law of public importance.
"Justice at the highest level should be transparent and the new Court will have a crucial role in letting the public see how justice is done."
4. Freedom of Information Act
The Freedom of Information Act 2000 gives everyone the right to access information held by public authorities, subject of course to a few exemptions.
The Act was designed to encourage greater openness, accountability and transparency in the public sector.
It only became effective on 1 January 2005, but it has already had a massive impact on government.
Visit Directgov for more information.
[For changes 5-10, read 10 Biggest Legal Changes Of The Decade, 2000-2009 (continued).]