During the post-grouping era from 1923 to 1948, the 4-6-0 wheel arrangement was used extensively by all of the Big Four British railway companies, especially by the Great Western Railway (GWR) and the London, Midland and Scottish Railway (LMS), who continued to develop new designs.

However, from the early 1930s, demands for more power and improved performance from express passenger locomotives led to the widespread introduction of 4-6-2 Pacific locomotives, where the trailing axle could support a larger firebox.
Since the reduced traction of the driving wheels was not a big disadvantage with relatively light passenger trains, the 4-6-0 was displaced from top-rank express services on most of the railways where they had been used, with the exception of the GWR who continued to build both mixed-traffic and express passenger 4-6-0s until nationalisation in 1948.
The GWR's 4073 Castle Class eventually consisted of 171 express passenger locomotives, built between 1923 and 1950.
The design was enlarged as the GWR's 6000 King Class, with thirty locomotives built between 1927 and 1930.

Several new mixed traffic 4-6-0s were also introduced:
The Southern Railway improved the LSWR's King Arthur class and introduced the Lord Nelson class, which was briefly the most powerful class in Britain.
Sixteen locomotives were built between 1926 and 1929.

The LMS introduced the 7P Royal Scot class, with 71 locomotives built between 1927 and 1930, and the 6P Patriot class, with 52 locomotives built between 1930 and 1934.
All of the Royal Scots and 18 of the Patriots were subsequently rebuilt in line with Stanier's practice and were very successful in this form.

The largest and most successful British 4-6-0 class was the LMS Class 5 Black Five, designed by William Stanier and consisting of 842 locomotives, built between 1934 and 1951.
Stanier also designed the LMS 6P Jubilee class, with 191 locomotives built between 1934 and 1936.

Charles Collett of the GWR developed Churchward's 1902 Saint class design into three further classes:
The GWR 4900 Hall class, with 259 locomotives built between 1928 and 1943.

The GWR 6800 Grange class, with eighty locomotives built between 1936 and 1939.

The GWR 7800 Manor class, with thirty locomotives built between 1938 and 1950.

Frederick Hawksworth later developed the Saint class design further, first with his GWR 6959 Modified Hall Class, with 71 locomotives built between 1944 and 1950, and then with his GWR 1000 County Class, with thirty locomotives built between 1945 and 1947.

The LNER inherited large numbers of 4-6-0 locomotives from its constituent companies, many of which were subsequently rebuilt, so that the company ultimately had sixty different classes and sub-classes with this wheel arrangement.
In addition, the company also introduced two new 4-6-0 classes.

The B17 class, designed by Nigel Gresley, of which 73 were built between 1928 and 1937.

The B1 class, designed by Edward Thompson, of which 410 locomotives were built between 1942 and 1952.
During the post-grouping era from 1923 to 1948, the 4-6-0 wheel arrangement was used extensively by all of the Big Four British railway companies, especially by the Great Western Railway (GWR) and the London, Midland and Scottish Railway (LMS), who continued to develop new designs.
However, from the early 1930s, demands for more power and improved performance from express passenger locomotives led to the widespread introduction of 4-6-2 Pacific locomotives, where the trailing axle could support a larger firebox. Since the reduced traction of the driving wheels was not a big disadvantage with relatively light passenger trains, the 4-6-0 was displaced from top-rank express services on most of the railways where they had been used, with the exception of the GWR who continued to build both mixed-traffic and express passenger 4-6-0s until nationalisation in 1948. The GWR's 4073 Castle Class eventually consisted of 171 express passenger locomotives, built between 1923 and 1950. The design was enlarged as the GWR's 6000 King Class, with thirty locomotives built between 1927 and 1930.
Several new mixed traffic 4-6-0s were also introduced:
The Southern Railway improved the LSWR's King Arthur class and introduced the Lord Nelson class, which was briefly the most powerful class in Britain. Sixteen locomotives were built between 1926 and 1929.
The LMS introduced the 7P Royal Scot class, with 71 locomotives built between 1927 and 1930, and the 6P Patriot class, with 52 locomotives built between 1930 and 1934. All of the Royal Scots and 18 of the Patriots were subsequently rebuilt in line with Stanier's practice and were very successful in this form.
The largest and most successful British 4-6-0 class was the LMS Class 5 Black Five, designed by William Stanier and consisting of 842 locomotives, built between 1934 and 1951. Stanier also designed the LMS 6P Jubilee class, with 191 locomotives built between 1934 and 1936.
Charles Collett of the GWR developed Churchward's 1902 Saint class design into three further classes:
The GWR 4900 Hall class, with 259 locomotives built between 1928 and 1943.
The GWR 6800 Grange class, with eighty locomotives built between 1936 and 1939.
The GWR 7800 Manor class, with thirty locomotives built between 1938 and 1950.
Frederick Hawksworth later developed the Saint class design further, first with his GWR 6959 Modified Hall Class, with 71 locomotives built between 1944 and 1950, and then with his GWR 1000 County Class, with thirty locomotives built between 1945 and 1947.
The LNER inherited large numbers of 4-6-0 locomotives from its constituent companies, many of which were subsequently rebuilt, so that the company ultimately had sixty different classes and sub-classes with this wheel arrangement. In addition, the company also introduced two new 4-6-0 classes.
The B17 class, designed by Nigel Gresley, of which 73 were built between 1928 and 1937.
The B1 class, designed by Edward Thompson, of which 410 locomotives were built between 1942 and 1952.
4-6-0