The rail break near Corby Glen in Lincolnshire was reported in September by a member of the public when they became concerned when "unusual levels of noise" were heard when trains passed a stretch of line in the area.
Shadow transport secretary Maria Eagle said that people living west of Cardiff had been "let down", and it would cost 20% more to electrify the stretch of line to Swansea under any future programme rather than as part of the current plan.