Everyone has the common law right to use the public highway. 

According to the law books, there is a right for all Her Majesty’s subjects at all seasons of the year freely and at their will to pass and repass the public highway without any let and hindrance.

And even now Downing Street remains part of the public highway. In principle, anyone – even the Conservative Chief Whip – has the legal right to pass up and down, and enter and exit, Downing Street without any obstruction or interrogation.  Indeed, to obstruct the public highway is an offence under section 137 of the Highways Act 1980 [2].  And an attempt to physically stop a pedestrian without good reason would also be a trespass to that person, for which he or she can sue.

But in practice, of course, no person can freely use Downing Street.   Iron gates have been in place since 1989 (and barriers were in place before then) and police officers are always at hand with firearms. 

How is this legally possible?  And what legal power, if any, was relied upon by the police officer in refusing to open the iron gates for Andrew Mitchell on his bicycle so that he could exit Downing Street?

The legal position is complicated. 

First of all, Downing Street itself is not a designated area for the purposes of anti-terrorist legislation [3] (and you see the relevant plan [4] which shows that neither the public highway nor the gates themselves are designated for the purpose).  So there must be some other legal basis for permitting what would otherwise be an obstruction to the public highway.

Before 2005, the police at the gates of Downing Street appeared to have relied entirely on common law powers in respect of potential breaches of the peace to stop people exercising their right to enter Downing Street.  Indeed in 1990, a minister said [5]:

Access to Downing street is controlled under police common law powers which allow them to take reasonable steps to preserve the peace and prevent threats to it.

This flimsy position (which was undoubtedly legally misconceived and unsustainable as a blanket position) was then formalised in 2008.  According to attachments to this obscure web page of Westminster City Council [6], an Order was made to:

(a)          prohibit vehicles and pedestrians from entering or proceeding in Downing Street at all times, except those authorised by the police;

(b)          prohibit pedestrians from entering or proceeding in that area of the footway forming the boundary between Downing Street and Whitehall, except those authorised by the police; and

 (c)           allow the police, at their discretion, to prohibit pedestrians from entering or proceeding in certain parts of Whitehall adjacent to the  Cabinet Office, the boundary with Downing Street and the Foreign & Commonwealth Office.

(You will notice that these powers refer to stopping people “entering or proceeding” on Downing Street, not exiting it as the hapless MP for Sutton Coldfield was then seeking to do, though this may be a moot point.)

This grandly titled WCC Traffic Management Order number 128 of 2008 in turn purports to rely on a range of statutory provisions in shutting the public out of Downing Street.  It is instructive to trace what these enabling provisions are, as it tells us something about how anti-terrorist law works in practice.

First, the Order cites a general power under section 6 [7] and Schedule 9 [8]of the Road Traffic Regulation Act 1984.  However, neither of these general provisions actually appear to give the Council quite the power to make an order as drastic as the one made.

The Order then refers to section 22C [9] of the same Act (introduced in 2005), and this makes all the difference.  This provides:

(1) An order may be made under section 1(1)(a) for the purpose of avoiding or reducing, or reducing the likelihood of, danger connected with terrorism (for which purpose the reference to persons or other traffic using the road shall be treated as including a reference to persons or property on or near the road).

(2) An order may be made under section 1(1)(b) for the purpose of preventing or reducing damage connected with terrorism.

(3) An order under section 6 made for a purpose mentioned in section 1(1)(a) or (b) may be made for that purpose as qualified by subsection (1) or (2) above.

So the public highway can be restricted by an order under the Road Traffic Regulation Act 1984.  In view of the 1991 terrorist attack on Downing Street [10], most people would agree that an interference with the universal right to travel up and down Downing Street is proportionate and justified.

But what actually was the legal power of the officer in refusing to allow Andrew Mitchell to exit Downing Street through the iron gates on his bicycle?  Every exercise of police power, of course, must have a legal basis.  Police do not actually have a general power to do as they will.  Would the police cite the 2008 Order or some common law power?  For, as the refusal has now led to a significant political crisis, it would be handy to know what the legal position had been.

So I asked the Metropolitan Police to tell me the actual legal basis of their officer's actions.  Their press office said they would not comment on security issues.  I pointed out that the applicable law would already be in the public domain, and that presumably there was a legal basis for their officer's refusal; but their response was the same - it was a security matter.  The impression which the refusal gave to me was that the Metropolitan Police press office either did not know or did not care what legal powers were used in a now controversial situation.

Thirteen years ago - eight years after the IRA's mortar attack - the police on the gates of Downing Street would happily let any member of the public on to Downing Street who presented no obvious danger and explicitly asked to do so.  I know this, as I did it myself: a friend and I went to look at the Downing Street Christmas Tree in 1999.

However, since 1999 (and especially since around 2005), both statutes and police powers have bitten away at the general and peaceful rights of people to do as they wish.  Perhaps there was a good reason to refuse the Tory chief whip his preferred form of exiting Downing Street that day in September 2012.  Perhaps opening the gates for him would have created some frightful security risk.  And there is no doubt that Mitchell's response to the refusal could have been far more graceful, whatever that response actually was.

It was only a trifle, after all, and he could have just nodded along as we all now are supposed to do; but annoyance at the unthinking use of police and security powers was surely a better reaction than merely nodding along.