Without going full-blown Keynesian, mass unemployment would persist, although with a slightly lower rate. The Gold standard was only the junior factor. The most important factors were the innate inefficiency and obsolescence of British heavy industries in the North, as well as industrial unrest and failing infrastructures, and these were market failures. So we need Yellow Book policies (Keynesian pump-priming was only a part of them) to tackle the root causes.
The City financiers, a strong interest group within the Tories, would not let a Tory PM or a Tory Cabinet to abandon Gold Standard until 1931, when it was clear than The Standard could not be kept.
Besides, the Tories were the only group that opposed railway nationalization during the 1920s, as even the Official Liberal Party committed to the cause. Churchill (Liberal) once said that the government must run the railway at loss to support industries. Besides, nationalizing railway would also allow greater development of national motorway system, which was never completed before ww2.
Launching Operation ROBOT would cause mass unemployment in the short-run and thus we need to butterfly away the horrible memories of the 1920s, which unlike the Depression was possible, to make it not a political suicide.