Hybrid Bills, such as that for Crossrail and now prospectively those for HS2, follow a distinct process before the UK Parliament. They provide a special means of authorising major infrastructure projects as well as providing the basis for legislating on other matters which affect particular private interests.

Hybrid bills affect particular interests differently from the population at large or other person or bodies in the same category or class. As such, they share some of the features of conventional public bills such as the annual Finance bill but also many of the features of private bills. In consequence, they are required to proceed as a cross between a public and a private bill (hence the designation 'hybrid'). Private bills are those bills promoted by outside interests (so not by the Government or an MP) and usually for a local purpose. Private bills were the means by which much of our Victorian infrastructure, public health and local government arrangements were authorised. Whilst gradually replaced by general powers or order-making procedures, some private bills are still promoted and they were still used extensively to authorise ports and railways until 1994.

Hybrid bills over the years have dealt with a very diverse range of subjects. Examples include bringing Caldy Island within local government arrangements for Pembrokeshire (1989-90), revising the governance and funding arrangements for the Museum of London (1985-86), making arrangements for the management of Trafalgar House which had been bequeathed to Nelson's successors (1946), the virtual nationalisation of the Bank of England in 1946 and the establishment of the London Passenger Transport Board (1931-33).

But what now most interests people about hybrid bills is the prospect of phase 1 of the HS2 railway (London to Birmingham) being authorised by hybrid bill, to be followed by a further hybrid bill for phase 2 (Leeds and Manchester). Assuming this happens, as the Government has indicated that it intends, HS2 will follow in the footsteps of other major infrastructure projects authorised in this way, including Crossrail (2005-08), High Speed 1 (1994-96), the Cardiff Bay Barrage (1991-93), the Second Severn Crossing (1990-92) and the Channel Tunnel (1986-87).

In some ways, this is quite surprising. Historically, railways had always been authorised by private bills (as mentioned above) but these were effectively abolished in 1994 when a new ordermaking procedure was devised. At that time, when promoting the HS1 hybrid bill for the Government, Jeremy Sullivan QC said that 'this is most probably the very last railway bill to be promoted through Parliament, thus bringing to an end over two centuries of Parliamentary select committee consideration of railway bills which began with the Middleton Colliery Railway bill in 1758'. What he had not counted on, however, was that Government would still see advantage in opting for the hybrid bill procedure even when, reflecting Parliament's reluctance to be involved with development authorisation, it had done away with private bills for the same purpose.

So why might it be that Government favours hybrid bills for large infrastructure projects of this sort? Various reasons can be given but, in essence, it appears to come down to a desire to secure maximum governmental control over what is a government project, whilst providing (relatively speaking) the prospect of greater speed and certainty of authorisation, a greater ability to over-ride ordinary policy and consenting procedures and less risk of legal challenge than with other non-parliamentary procedures.

But, even when the government of the day has a healthy built in majority, it is not all plain-sailing in Parliament. The process is complex and full of pitfalls. As Cabinet Office Guidance on public legislation advises: 'Generally the procedure is longer and more expensive [than for Public Bills]..., so hybrid Bills are best avoided where possible.'

Like private bills, hybrid bills are subject to special procedures set out in the Private Business Standing Orders. This means, amongst other things, that they have to be subject to prior notices to affected parties, public advertisement and the deposit of prescribed documents. These days, in the case of an infrastructure project like HS2, the documentary requirements include a detailed Environmental Impact Statement as required for development projects by European Law. Once these processes have been completed and the Bill is presented, those concerned with the bill's contents can then petition and have their case heard before a specially formed committee which is constituted after Second Reading of the Bill takes place and before the bill is referred in the ordinary way to a public bill committee (or Committee of the Whole House in the Lords). Unless the bill is referred to a joint committee of both Houses (which has not happened in modern times), they can also petition for the first time, or do so again, when the Bill passes to the second House (usually the House of Lords). So, there are potentially two opportunities to petition.

Whilst Parliament can of course alter the bill during its passage, the making of any material modification to the project after the bill has been presented which might adversely affect a third party usually means first repeating the notification, documentation and petitioning processes through the promotion of what is called an Additional Provision. That tends to cause substantial delay.

Hybrid bill procedure has not been the subject of any general review or wholesale reform since 1948 (though a modernised hybrid bill procedure was devised for the Scottish Parliament). As a result, there are aspects of the procedure which can appear rather odd to the modern eye.

The process has certainly not kept pace with all the checks and balances and best practice principles that have been devised for development consenting procedures outside Parliament.

For example, it remains the case that provision is only made for Parliament to consider representations from those affected by the bill if those affected present a petition in a prescribed form, either in person or through a registered agent (but not eg by email or post) and after paying a £20 fee. Even then, they have no absolute right to be heard as what are known as 'locus standi' rules, many dating from the Victorian era, mean that only those considered to be 'specially and directly affected' are strictly entitled to be heard on a petition and eg specially formed action groups tend to be excluded.

Another particularly distinguishing feature, when compared with other development authorisation processes, is the convention that the principle of proceeding with the project the subject of the hybrid bill is determined at Second Reading, and so in advance of consideration of third party (petitioners') representations at the Committee Stage or of full consideration of environmental impacts. This precludes those affected from challenging, through their petitions and at the Committee stage, the needs case for the project which may be all they really want to do. It also presents problems for environmental assessment.

The select committee stage, when petitions are considered, traditionally takes a form similar in a number of respects to a public local inquiry, with the Government and other parties being represented by legal counsel, other professionals or (frequently in the case of local residents) in person and with each side calling witnesses and making opening and closing speeches. Ironically, the public inquiry procedure has now fallen out of favour for major infrastructure authorisation outside of Parliament where it now takes more of a written and investigative as opposed to adversarial process. Those used to public inquiries are also likely to be surprised by a number of aspects of the parliamentary procedure.

These include the individualistic approach of the Committee Members, who are politicians not professional inspectors or assessors, the tendency for evidence not to be tabled in advance for consideration and the programming of proceedings which tends to make little allowance for those with other and conflicting commitments.

Various mechanisms have been tried on recent hybrid bills to help address deficiencies in the process and smooth their passage. These have included prescribing additional documentary requirements by Standing Order, instructions to select committees (both to widen and to narrow their remit), avoidance of locus standi challenges, sitting in parliamentary recesses and arranging sittings in the localities affected outside Parliament. The Government and the House Authorities are no doubt now giving thought to how best to advance and build on such practices to help ensure that HS2 does not break the system nor the system break HS2.

In the case of Crossrail, the general consensus certainly appears to be that the system worked pretty well, that the project particulars in that case were properly scrutinised and that, by and large, affected third parties felt that they received a fair hearing. HS2 however may well present a much stiffer challenge, not least to the MPs who are prevailed upon to constitute the select committee (which in Crossrail's case, sat for 84 days). Despite it meaning that they may well have little wish to be involved, those MPs nominated for the select committee must have no constituency interest in the Bill.

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