Why do Acts of the UK Parliament still start with a lengthy bombastic sentence?
<p>Source: Rebecca Gowers. <a href="https://www.amazon.co.uk/Plain-Words-Rebecca-Gowers/dp/0241960347" rel="nofollow noreferrer"><em>Plain Words</em> (2014 ed)</a>. p. 76 Top.</p>

<p>Can't the hackneyed sentence (in bold, below) be shortened? Why not something less pompous?  </p>

<blockquote>
  <p>  The first affects only the official. It is tempting to cling too 
  long to outworn words and phrases. The British Constitution, 
  as everyone knows, has been shaped by retaining old forms 
  and putting them to new uses. Among the old forms that we 
  are reluctant to abandon are those found in State documents. 
  Every Bill begins with the words:</p>
  
  <blockquote>
    <p><strong>'Be it enacted by the Queen's Most Excellent Majesty, by and with the advice and consent of the Lords Spiritual and Temporal, and Commons, in this 
    present Parliament assembled, and by the authority of the same, as follows...'.</strong></p>
  </blockquote>
  
  <p>It ends its career as a Bill and becomes an 
  Act when the Clerk of the Parliaments is authorised by the 
  Queen to declare 'La Reine le veult'. <strong>That is all very well, 
  because no one ever reads these traditional phrases; they are 
  no longer intended to convey thought from one brain to 
  another.</strong> And none of us would much like the official to say,  'That's OK by Her Majesty'. But officials, living in this 
  atmosphere, and properly proud of the ancient traditions of 
  their service, sometimes allow their own style of writing to be 
  affected by it—<em>adverting</em> and <em>acquainting</em> and <em>causing to be 
  informed of same</em>. There may even be produced in the minds of 
  some officials the feeling that a common word lacks the 
  dignity that they are bound to maintain. </p>
</blockquote>

<p>From <a href="https://en.wikipedia.org/wiki/List_of_enacting_clauses" rel="nofollow noreferrer">Wikipedia</a>:</p>
<blockquote>
<p>An <strong>enacting clause</strong>, or <strong>enacting formula</strong>, is a short phrase that introduces the main provisions of a law enacted by a legislature. It usually declares the source from which the law claims to derive its authority. In many countries, an enacting formula is not considered necessary and is simply omitted.</p>
<p>The simplest enacting clauses merely cite the legislature by which the law has been adopted; for example the enacting clause used in Australia since 1990 is &quot;The Parliament of Australia enacts&quot;. Alternatively an enacting clause may invoke the ultimate sovereign. For example, California, based on the principle of popular sovereignty, has the following enacting clause: &quot;The People of the State of California do enact as follows.&quot;</p>
</blockquote>
<p>For example, Acts of the US Congress begin with words not unlike those of Acts of Parliament:</p>
<blockquote>
<p>Be it enacted by the Senate and House of Representatives of the
United States of America in Congress assembled</p>
</blockquote>
<p>UK statutory instruments go further, stating not only who made the order, but also which legislation provided the power to make this order. To take a <a href="http://www.legislation.gov.uk/uksi/2018/654/made" rel="nofollow noreferrer">recent example</a> at random:</p>
<blockquote>
<p>The Secretary of State for Education makes the following Order in exercise of the powers conferred by section 129(1) of the Education Reform Act 1988</p>
</blockquote>
<p>From these, one might surmise that the purpose of these sentences is to convince the reader that the person or body issuing the legislation has the power to do so.</p>
<p>For most statutory instruments, the power to make them comes from Acts of Parliament, and so the specific section(s) of the those Acts are stated. For Acts of Parliament themselves, it is taken as read that the Queen, Lords and Commons acting together (or more formally, the <a href="https://en.wikipedia.org/wiki/Queen-in-Parliament" rel="nofollow noreferrer">Queen-in-Parliament</a>) have the power to legislate, so it is sufficient to merely state that is they who have done so - and similarly for the US Congress and other legislatures.</p>
<hr />
<p>In response to edits in the question:</p>
<blockquote>
<p>Can't the hackneyed sentence ... be shortened?</p>
</blockquote>
<p>Yes it could, as evidenced by the fact that not all countries use an enacting clause at all, and some of those that do have shorter, simpler ones.</p>
<blockquote>
<p>Why not something less pompous?</p>
</blockquote>
<p>Why should they?</p>
<p>One shouldn't underestimate the role of tradition in the UK constitution - indeed it's held together in part by unwritten conventions whose long use has solidified them into something like law.</p>
<p>As mentioned in the question, bills don't become acts until they've been assented to by a hereditary monarch, which is indicated by a clerk uttering a statement in Norman French. Compared to that, what's wrong with acts starting with a grandiose statement?</p>
<hr />
<p>Incidentally, if you thank that's pompous, then you'll enjoy the enacting clause which appears at the top of UK <a href="http://www.legislation.gov.uk/ukpga/2018/3/introduction/enacted" rel="nofollow noreferrer">Finance Acts</a>:</p>
<blockquote>
<p>Most Gracious Sovereign</p>
<p>WE, Your Majesty’s most dutiful and loyal subjects, the Commons of the United Kingdom in Parliament assembled, towards raising the necessary supplies to defray Your Majesty’s public expenses, and making an addition to the public revenue, have freely and voluntarily resolved to give and to grant unto Your Majesty the several duties hereinafter mentioned; and do therefore most humbly beseech Your Majesty that it may be enacted, and be it enacted by the Queen’s most Excellent Majesty, by and with the advice and consent of the Lords Spiritual and Temporal, and Commons, in this present Parliament assembled, and by the authority of the same, as follows:—</p>
</blockquote>
<p>Finally, context is everything. I would strongly recommend watching a recording of the <a href="https://en.wikipedia.org/wiki/State_Opening_of_Parliament" rel="nofollow noreferrer">State Opening of Parliament</a>. In addition to all the pomp and circumstance, the main event where is the Queen - wearing a priceless bejewelled crown, sitting on a golden throne under a golden canopy, watched by Peers of the Realm dressed in ermine robes - reads a speech prepared by the government, in the chamber of the House of Lords, with its golden ceiling, intricate carvings, statues and stained-glass windows. Compared to that, a few extra words at the start of an Act seems kind of modest, don't you think?</p>

united-kingdom bills