“The accumulation of all powers in the same hands … [is] the very definition of tyranny” (Madison) 
The protection of individual liberties and rights is one of the key objectives of any constitution. In order to protect those freedoms, the constitution needs to prevent one part of the state becoming too powerful.
This answer will examine what is meant by the ‘UK constitution’; it will then examine briefly what is meant by a ‘ separation of powers’ and use this doctrine to identify areas where power may to be too concentrated. It will then analyse how far Barendt’s “network of rules and principles” in the constitution can control the potential danger in these areas, examining in particular the control exerted by the government over parliament. Finally, it will evaluate the judiciary’s attempts to counterbalance this executive power and the recent boost they have received from the Human Rights Act 1998.
The UK constitution has evolved over hundreds of years and is not codified, despite having certain written elements  . This means one cannot look in a single document – as one might in a state with a codified constitution like the US – to discover whether there are sufficient safeguards against excessive power within a particular organ of the state. The current UK constitution is to be found within statutes and case law, conventions and royal prerogatives, each of which will need to be examined to determine if they guard against concentrations of power.
What then are the state powers that need to be separate and controlled? The modern exposition of the ‘separation of powers’ doctrine comes from Montesquieu  . He states in essence that liberty is best protected when the three organs of state – the executive, legislature and judiciary – have separated functions. As hinted at by the quotation in the essay title, the exact meaning of ‘separation of powers’ has been the subject of much academic debate, which is beyond the scope of this essay. Broadly speaking, ‘separation of powers’ can be seen either in ‘strict’ terms i.e. in the overlap of personnel and functions between the organs of state; or, more loosely, by additionally considering the checks and balances which moderate the power of the various organs of state in practice.
It is uncontroversial to state that “there is no absolute separation of powers in this country”  in the strict sense. The key members of the executive – the prime minister and his cabinet – are drawn wholly from within the ranks of the legislature; this leads to “the nearly complete fusion of the executive and legislative powers”  . A majority government can effectively both create and approve new laws:
“..[T]he function of Parliament today is to make party political noises about the legislation placed before it by the executive and then, with very rare exceptions, to rubber-stamp it” 
Additionally, ministers can create delegated legislation. Although Parliament must approve any such legislation this further undermines the separation of powers and represents a potential excessive concentration of power.
Whilst the near fusion of executive and legislature represents the most obvious threat to ‘separation of powers’ in the UK, there are other areas of overlapping personnel and function which I will briefly deal with.
Personnel overlaps between the judiciary and other organs of state have largely been removed following the Constitutional Reform Act 2005: the Supreme Court has replaced the appellate function of the House of Lords and the office of Lord Chancellor no longer has his former role as head of the judiciary. This strengthens the independence of the judiciary on paper, though whether it has much practical effect is yet to be seen.
As regards overlapping functions, there is no doubt that, in a legal system based on the doctrine of precedent, the judiciary perform a quasi-legislative function on a daily basis. Whilst there are examples where judges have clearly overstepped the line between creative interpretation and law-making (e.g. R v A  ; Shaw v DPP  ), these appear to be counterbalanced by numerous examples where judges have reemphasised Parliament’s supremacy as regards the legislative function (e.g. Malone v MPC  ; Bellinger v Bellinger  ). On balance, the extent of the judiciary’s functional overlap into the legislative branch seems moderate in comparison to the executive’s near total control of the legislature, and it is on this latter issue that I will now concentrate.
This potentially dangerous concentration of power in the executive function is made more dangerous because the controls in the UK constitution against excessive executive power appear increasingly ineffective.
Statutory controls have limited effect: since the Parliament Acts of 1911 and 1945, the House of Lords has no veto over most legislation. As the traditionally independent upper house is gradually reformed and replaced with selected (and in the future, elected) members, its independence from party-political pressure is ever-diminishing. The House of Commons (Disqualification) Act 1975 attempts to control the size of the executive by limiting the number of paid ministers but the increasing power of the party whip system mean that a majority government can effectively control what legislation is passed.
Parliamentary scrutiny over the executive also appears toothless: Question Time has become little more than a public posturing exercise. The supposed restraints brought by the conventions of individual and collective ministerial responsibility do not bear much scrutiny: when Estelle Morris tendered her resignation after overwhelming evidence of departmental incompetence, the Prime Minister attempted nonetheless to persuade her to stay  . Clare Short may have allegedly resigned over the Iraq war on the issue of ‘collective ministerial responsibility’ but in reality the Prime Minister allowed her to stay in government for several weeks after denouncing government policy in public  , suggesting that the resignation had more to do with political expediency.
Democratic restraints on the executive are also severely limited given the current ‘first past the post’ electoral system and the level of public participation in elections. Recent general elections have had an average turnout of c.60%, meaning that the votes of c.20% of the electorate delivered the latest government an overall majority in Parliament  .
Barendt sums up the situation thus: “The truth is that there is no effective separation of powers between legislature and executive in the United Kingdom in the sense of a system of ‘checks and balances’” 
With today’s legislature unable to control the powers of a majority government under the UK’s constitution, the restraining role falls increasingly to the judiciary. The courts have made several strong ‘separation of powers’ judgments emphasising that legislation cannot be ignored by the executive (R v Secretary of State for the Home Department ex p Fire Brigades Union  ); that the determination of the courts must be followed even by members of the executive (M v Home Office  ); and that the executive cannot perform judiciary functions (e.g. R (on the application of Anderson) v Secretary of State for the Home Department  ; T v UK  ). The courts have also shown themselves prepared to review even those constitutional areas traditionally believed to be firmly within the realm of politics. The GCHQ  judgment showed that by 1985 the judiciary were prepared to scrutinise most areas of royal prerogative
In the last decade, the judiciary’s powers vis-à-vis the executive have been significantly boosted by the Human Rights Act 1998, as the courts can now challenge legislation directly because it violates human rights, and not just because the executive have acted ultra vires. The courts have used this new power in several areas, perhaps most revealingly in the ongoing battle regarding anti-terrorism legislation. In A & Others v Secretary of State for the Home Department  , the courts declared detention without trial incompatible with the ECHR; the government’s response inter alia was to create so-called ‘control orders’; the courts have also ruled many of these to be incompatible for various reasons (e.g. Secretary of State for the Home Department v JJ  ; Secretary of State for the Home Department v AF  ). The Supreme Court continues the trend to this day, rejecting Treasury freezing orders on terrorist assets (A v HM Treasury  ). It is clear that the judiciary have now extended their role to ensuring the legality of government action even in areas of national security – a clear change from the days of Liversidge v Anderson  deference.
In summary, the UK’s evolving and uncodified constitution has gradually allowed too much power into the hands of the executive at the expense in particular of Parliament. Although the judiciary, strengthened by the Human Rights Act, appear to be an effective counterweight at present, the lack of a codified constitution means that this situation is in no way guaranteed for the future.