Boris Johnson's chaotic time in office exposed weaknesses in the UK's political system that have damaged public trust and the country's international reputation, a major review has found.
A report by the Institute for Government (IfG) called for urgent reform following a tumultuous period which has seen MPs test or break constitutional principles - including the former prime minister.
It said the UK constitution - which refers to the rules and laws that establish and underpin a political system - was an outlier on the world stage because it lacked "a central, codified source" and rested on the concept of parliamentary sovereignty.
This means there has been a historic reliance on "self-restraint from political actors rather than legal checks".
However recent events have shown the willingness of MPs to push those boundaries, raising questions about the adequacy of checks and balances to "constrain political power", the report said.
It cited the "misdemeanours" of Mr Johnson as an example of how the effectiveness of current arrangements are vulnerable to being tested.
The report, co-authored by Cambridge University's Bennett Institute for Public Policy, said: "Boris Johnson's attempt to prorogue parliament, disregard for the Ministerial Code, willingness to break the law while in office and misleading of parliament were all examples of a prime minister who, in the words of his cabinet secretary, believed he had 'a mandate to test established boundaries'.
"Not all of his misdemeanours were unprecedented; but his premiership shone a light on existing problems within the UK's governing arrangements, and heightened the concern that there has been a steady erosion of the tacit norms on which government in the UK rests."
The 18-month review was supported by an advisory board including former Conservative ministers Sir Robert Buckland and Sir David Lidington, shadow leader of the House of Lords Baroness Smith of Basildon and former Labour Mayor of Liverpool Joanna Anderson.
It said that within the wider global context of "deepening public suspicion of governmental institutions and heightened political polarisation", events over the last decade "have placed the UK's constitution under immense strain, underlining the urgent need for serious thinking about the nature and trajectory of the UK's constitution".
UK 'facing crisis in institutions'
The report says: "The UK is facing a crisis in trust in politics and political institutions.
"Recent political instability has undermined the UK's reputation as a stable democracy, damaging its international reputation and, as a consequence, its economic prospects."
As a key example of the need for change, the report cites ministers' previous willingness to override international law over the implementation of the Northern Ireland protocol.
Despite senior civil servants resigning, interventions from former prime ministers and concerns expressed by the international community, the legislation passed the House of Commons in just over a month, with not a single rebellion from the Conservative backbenches.
A series of recommendations for change include establishing a new parliamentary committee on the constitution, which should have the power to delay legislation.
The review also said parliament should have a more extensive scrutiny process for new constitutional bills to ensure proposals are "thoroughly tested and attract cross-party support", alongside clarification on the role of the civil service and strengthening its capacity to give constitutional advice.
Integrating public engagement through citizens' juries and assemblies was also recommended.
Director of the IfG Hannah White said: "Our recommendations are intended to ensure that any politician considering changing the UK constitution is supported with robust advice, and to ensure that the UK constitution is changed only with appropriate consideration and public support."