Strictly speaking, the Crown - as in the Monarchy - is. Within British constitutional law, the Crown has a role to play in the legislative process and is considered part of the parliamentary institution, commonly referred to today as the Queen-in-Parliament. In order for a law to be realised as statute after passing both houses of Parliament, it must be granted Royal Assent; for this reason British law usually begins with the phrase "Be it therefore enacted by the King/Queen's most Excellent Majesty" (or a variation thereupon). See an historic example in this legislation abolishing slavery in 1833. The Crown also has the power to implement secondary or delegated legislation, which unlike primary legislation, stands so long as it is not disapproved of by Parliament; that kind of legislation is usually limited, and usually concerns the details of how a primary piece of legislation that has passed Parliament will be implemented. By virtue of predating Parliament, the Crown is the oldest part of it.

It thus has a significant, if in recent history ceremonial, role to play in the legislative process and is considered one of the three components of Parliament along with the House of Commons and the House of Lords. Primary legislation may only pass if all three components are in agreement, though in practice since 1911 the House of Commons has held legal and functional supremacy over the House of Lords on most issues (a power strengthened in 1949; a veto by the Lords since then only delays a law by one year). Constitutional and democratic conventions likewise mean the last time Royal Assent was denied was in 1707; in practice, between 1707 and 1911 only the consent of the two Houses of Parliament were necessary to pass legislation, and since 1911 it has been possible to pass legislation with just the support of the House of Commons (though this has been rare).

Within the House of Commons, the oldest continuous position would presumably be that of Member of Parliament for Lincoln, which pre-dates even the existence of the Speaker of the House. Lincoln is the only constituency that has returned members in every election to the House of Commons since the first in 1265 - so last year's election marked the 750th anniversary of Lincoln sending representatives to Parliament. The City of York constituency was previously tied with it until the expansion of its population meant that the constituency was split into two by the Fifth Periodic Review in 2007, meaning the City of York had continuous representation in Parliament for 745 years (1265 - 2010).

Lincoln had 74,133 voters in 2015, meaning it is the right size to survive the possible forthcoming change to the law in 2018 which would limit the size of constituencies to between 72,810 and 80,473 voters (and cut the size of the House of Commons by 50 seats). On the unlikely chance that Lincoln were to be abolished, there are several constituencies still in existence like Guildford or Ipswich, first created in 1295, that would jointly inherit the title of oldest constituency. Those positions would still be older than the position of Speaker, which formally dates only to 1377; Black Rod dates to about 1348.