Extension of the Broad Gauge System—Break of Gauge—Royal Commission on the Gauge of Railways, 1845
As has been before mentioned, extensions and branches on the same gauge, to all of which Mr. Brunel was engineer, were projected and ultimately carried out, in accordance with the original scheme of the undertaking, to Exeter, Plymouth, and Cornwall, and to Gloucester, Hereford, and South Wales, as well as to Oxford, Windsor, and other towns in the immediate neighbourhood of the line.
About 1844, the attention of the Company began to be directed to projects involving extensions of a much more serious character, and which were destined to have a powerful influence on the position of the gauge question. During the railway mania, the Great Western Company found it impossible to stand aloof from the contests which were going on around them, and thought it necessary, in order to protect their own interests, to extend their lines beyond the district to which they had originally intended to confine themselves.
At the general meeting in August, an extension from Oxford to Rugby was determined on, as ‘of the greatest importance to the Great Western line.’ About the same time a broad-gauge line was promoted from Oxford to Worcester, and thence by Kidderminster and Dudley to Wolverhampton, in order to open an immediate communication with the Staffordshire and Worcestershire districts. There were also rival projects on the narrow gauge, promoted by the London and Birmingham Company; and the competing plans were referred, as was the custom at that time, for the examination of the Railway Department of the Board of Trade.
In regard to the communication from north to south, through Oxford, the question was, where the break of gauge should be.  The Board of Trade saw nothing in the relative merits of the gauges to determine this question, and from commercial considerations, they recommended that the change of gauge should be made at Oxford. On this and other grounds they considered that the narrow gauge schemes to the north of Oxford were preferable to those of the Great Western Railway.
The rival schemes then went before Parliament, and after a protracted enquiry, obstinately fought between the parties, the decision was given in favour of the Great Western lines, contrary to the recommendation of the Board of Trade. It was, however, stated by the chairman of the Commons Committee that the decision had been founded on the local and general merits of the respective lines, without any reference to the comparative merits of the two gauges. On this account some peculiar provisions were made in the Acts; for though the lines were sanctioned on the broad gauge, the proprietors were bound also to lay down narrow gauge rails upon them, if required to do so by the Board of Trade. At the same time the House of Commons, on the motion of Mr. Cobden, passed a Resolution praying her Majesty to refer the gauge question to a Royal Commission.
A Commission was issued in July; the Commissioners being three in number—Sir J. M. Frederic Smith, R.E.; Mr. G. B. Airy, Astronomer Royal; and Professor Barlow, of the Royal Military Academy, Woolwich. They took a large amount of evidence, both oral and documentary, and made some examinations of the working of the two gauges. Their report was presented to Parliament early in the session of 1846.
Of forty-eight witnesses, thirty-five were advocates of the narrow gauge; and against these were arrayed but four champions of the broad gauge, all officers of the Great Western Railway:—Mr. Charles Alexander Saunders, the secretary; Mr. Seymour Clarke, the traffic superintendent; Mr. (now Sir Daniel) Gooch, the locomotive superintendent; and Mr. Brunel.
The report was of considerable length, and in it the Commissioners addressed themselves to three heads of enquiry, viz.:—
1. Whether the break of gauge was an inconvenience of so much importance as to demand the interference of the legislature.
2. What means could be adopted for obviating or mitigating such inconvenience.
3. Considerations on the general policy of establishing a uniformity of gauge throughout the country.
The general conclusions arrived at on these points were thus summed up by the Commissioners:—
1. That, as regards the safety, accommodation and convenience of the passengers, no decided preference is due to either gauge, but that on the broad gauge the motion is generally more easy at high velocities.
2. That, in respect of speed, we consider that the advantages are with the broad gauge; but we think the public safety would be endangered in employing the greater capabilities of the broad gauge much beyond their present use, except on roads more consolidated, and more substantially and perfectly formed, than those of the existing lines.
3. That, in the commercial case of the transport of goods, we believe the narrow gauge to possess the greater convenience, and to be the more suited to the general traffic of the country.
4. That the broad gauge involves the greater outlay, and that we have not been able to discover, either in the maintenance of way, in the cost of locomotive power, or in the other annual expenses, any adequate reduction to compensate for the additional first cost.
Therefore, esteeming the importance of the highest speed on express trains for the accommodation of a comparatively small number of persons, however desirable that may be to them, as of far less moment than affording increased convenience to the general commercial traffic of the country, we are inclined to consider the narrow gauge as that which should be preferred for general convenience, and therefore, if it were imperative to produce uniformity, we should recommend that uniformity to be produced by an alteration of the broad to the narrow gauge….
Guided by the foregoing considerations, the Commissioners recommended that 4 feet 8½ inches should be fixed by law as the standard gauge of the country; and that as to the existing broad gauge lines, either they should be altered to the narrow gauge, or some course adopted which would admit of narrow gauge carriages passing along them. 
This adverse report was a great surprise to the supporters of the broad gauge system, as rumours had led them to hope for a different result. Immediately after its appearance, several documents were published, containing powerful and severe strictures on the proceedings and opinions of the Commissioners. The most important of these was written by Mr. Saunders, Mr. Daniel Gooch, and Mr. Brunel. It occupied fifty closely printed folio pages, and was entitled, ‘Observations on the Report of the Gauge Commissioners, presented to Parliament.’ To this, ‘Supplemental Observations’ were added, after the publication of the Evidence and the Appendix to the Report.
In the conclusion of the ‘Observations’ the writers gave a summary of the points they considered to have been proved in the controversy, namely—
That the question of ‘break of gauge’ originated as a cloak to a monopoly.
That even if the gauge were uniform, through trains would be impracticable.
That the transfer would be of little inconvenience.
That any advantage of small waggons was applicable to the broad gauge, but that the advantage of large waggons was not applicable to the narrow.
That the competition between the two systems was advantageous.
That the final recommendations of the Commissioners were at variance with their separate conclusions.
That it would be unjust to refuse to allow the broad gauge to be laid down on lines for which it was already sanctioned by Parliament.
That the enquiry before the Commissioners was not properly conducted, and that consequently no legislation ought to be founded on it.
That the data published by the Commissioners were often wrong, and in some cases led to the reverse of their conclusions.
That greater economy was proved on the broad gauge.
That the broad gauge was superior in the points of safety, speed, and conveyance of troops.
That the experiments made in the presence of the Commissioners had demonstrated beyond all controversy the complete success of the broad-gauge system.
For these and other reasons, a strong protest was made against any legislative interference with the broad-gauge system.
A reply was published to these arguments; and during the controversy a large number of pamphlets, articles, and other publications appeared on both sides.
 The inconveniences of a break of gauge had already been brought into notice. One of the narrow-gauge companies, the Midland, worked two existing lines of railway, one between Birmingham and Gloucester, laid on the narrow gauge, and another between Bristol and Gloucester, on the broad gauge; and thus there was a break of gauge at Gloucester.  It should, however, be added, that the Commissioners had stated in the body of their report: ‘We feel it a duty to observe here, that the public are mainly indebted for the present rate of speed, and the increased accommodation of the railway carriages, to the genius of Mr. Brunel and the liberality of the Great Western Company.’