After World War I passenger traffic as well as goods and mineral business declined further. Worse was to come, for the Railways Act 1921 put both the G&SWR and the Caledonian/L&AR routes under common ownership of the new London Midland and Scottish Railway (LMS). The former G&SWR routes had better connectivity for the now sparse traffic, and on 28 July 1930 the first closure, to passenger traffic on the Irvine branch, took place. Total closure of the branch followed on 30 December 1930. The Kilbirnie branch too closed in 1930.