After the L1, Ivatt developed another tank locomotive for the GNR for use on the city lines of London. In order to be better suited for higher speeds, there were only three driving axles with 5 ft 8 in wheels. As with the L1, the first example of the N1 was too heavy for the Metropolitan Lines. In the following locomotives, the axle load on the driving axles was reduced by placing more weight on the trailing axle. This was done by moving them further back and shortening the front water tanks and accommodating more water behind the cab. A total of 56 were produced by 1912, all but six of which were again equipped with a condenser. The latter six were used in the West Riding of Yorkshire.

Initially, most N1 remained in service in London. During World War I, two were sold to the War Office, one of which was used to build an armored train. In the years that followed, superheaters of the Schmidt type were installed in eleven locomotives. From 1920 Gresley's N2 replaced the N1 in passenger service. The N1 continued to operate in north London, but mostly to haul empty passenger coaches and freight trains. After the locomotives had come to the LNER, the remaining ones were fitted with Robinson type superheaters and the eleven which had already been converted were also refitted. Gradually more locomotives came to Yorkshire where the condensers were removed. Most ended up with British Railways, the last being withdrawn in 1959.