During the Conservative governments of 1979-1997, there were no major constitutional changes, apart from those produced due to membership of the European Community and by agreements with the Irish Republic over Northern Ireland.. When Labour gained power in 1997, they introduced quite a few reforms in their time until 2010.
Some of these were reforms such as the Human Rights Act 1998 which incorporated the EU laws on Human Rights into UK Law. I would define this as a success as it meant that if we were to leave the European Union, everyone would not lose their basic human rights. This is a form of modernisation as it brought the UK parliament more in line with other western democracies.Labour also devolved more power to the Scottish Parliament and the Welsh Assembly in the the Scotland Act 1998 and the Government of Wales Acts, 1998 and 2006. This is also a success as it is a form of decentralisation.Another successful reform introduced by Labour was the House of Lords Reform Act, 1999 which removed most of the hereditary peers. This is a form of democratisation and it was definitely a success although Labour also tried to make the House of Lords wholly elected which ended up not happening which was one of their failures.
Another success of the Labour government was the Constitutional Reform Act, 2010 which set up the UK Supreme Court and increased the independence of the Judiciary. This is a form of democratisation as it meant that there was more of a separation of powers between the three branches of government.Overall, the Labour government mainly had successful constitutional reforms with the only failures being not fully removing the hereditary peers from the House of Lords and not making it a fully elected chamber. However, when the Conservative/Lib Dem coalition took over in 2010, they did not have as much success with their constitutional reforms.
They still had a few successes though such as passing the Fixed Term Parliament Act in September 2011. This removed the Prime Minister’s power to use the Royal Prerogative to call an early General Election, ensuring that Parliaments would last 5 years. It also codified the convention that when a government was defeated on a vote of confidence in the Commons, the Prime Minister had to resign, usually forcing an election.
It also meant that now a vote of no confidence has to be confirmed by a second vote within 2 weeks. There can also be an early General Election if two thirds of MPs vote for one. This was the way in which Theresa May was able to call her early General Election in 2017 which means that this reform was not a complete success as it is clearly still possible for Prime Ministers to call early General Elections.
Another success was the Scotland Act, 2012 which devolved more power to the Scottish Parliament. This was a form of decentralisation.However, most other reforms were unsuccessful such as proposed reform of changing the voting system for elections from “First-past-the-post” to “The Alternative vote” which required approval in a referendum. It was a form of democratisation as it would mean a move to a more proportional representation system but in 2011 a referendum was held with a large majority of people saying no to the change.
That meant that this was definitely one of the failures of the coalition government.Another failure of the coalition government was the House of Commons reform which was meant to reduce the number of MPs to 600 and make constituencies roughly the same size in terms of voting population. This was blocked in the Commons and so was definitely a failure for the coalition government.In conclusion, I think that overall the Labour government from 1997-2010 had more successes than failures but the Coalition government from 2010-2015 definitely had more failures than successes and I would say that over the entire period of 1997-2015, in general there were more successful constitutional reforms than failures in all areas of decentralisation, democratisation and modernisation.