An investigation into over-running rail engineering work during Christmas and New Year is to examine whether the hold-ups threaten the punctual delivery of an important upgrade programme.

The Office of Rail Regulation probe into the overruns at Rugby, London Liverpool Street and Glasgow’s Shields Junction will look at whether plans for upgrade work on the west coast main line will deliver in time for scheduled timetable improvements in December. New tracks need to be laid between Rugby and Stafford, while junctions at Rugby need to be remodelled before Virgin Trains can start running services more frequently and faster on the key London-Glasgow route.