The large number of new railway schemes being authorised, both broad and otherwise, caused an economic depression in the second half of the 1840s, which made it difficult to raise the money needed to build even those lines already under construction. The South Devon line was not complete to Plymouth until 1849, and the South Wales was only finished in 1856.
In the meantime, Parliament had formed its Gauge Commission. In 1846 it recommended that the 4ft 8½in gauge be the standard in future, however the broad gauge line authorised in 1845 from Oxford towards Rugby was to be built as mixed gauge so it could carry both broad and narrow trains.
This line to the north reached as far as Wolverhampton in 1854, but within a couple of months the GWR had purchased 4ft 8½in gauge lines that allowed it to run further north, and after that it started to lay more mixed lines to save it the expense of transferring goods where there was a break of gauge. These reached as far as Paddington by 1861, and the lines from Oxford to Wolverhampton carried only narrow trains from April 1869.
In the south west, the line from Chippenham to Weymouth, authorised in 1845, was completed in 1857. Two years later the Royal Albert Bridge was completed allowing broad gauge trains to reach Truro, but the line beyond had already opened with just narrow tracks; this was widened to mixed tracks in 1866 to allow through trains from Paddington to Penzance.
However, work soon started on converting other broad gauge lines to 4ft 8½in. The first was the short Hereford branch in 1869, but in 1872 the route from Swindon through South Wales was converted, and that to Weymouth in 1874. Mixed gauge extended along the main line as far as Exeter by 1876.
One final broad gauge line was built in the far West; the St. Ives branch opened on 1 June 1877, 39 years after the first broad gauge train had steamed out of Paddington. By now broad gauge trains only ran from Paddington to Penzance (using the mixed gauge as far as Exeter and beyond Truro, and on various branch lines. Several of these were converted during the years to 1891, which just left Exeter to Truro and associated branch lines routes. In a massive final push, these were all narrowed over the hectic weekend of May 21–22, 1892, - and the broad gauge was no more !
