Northern rail passengers are used to delays — the introduction of new timetables led to months of disruption, which has yet to be resolved. But an announcement about the future of the £21B HS2 northern spur from Birmingham to Manchester and Leeds seems to be trapped in another kind of delay. Or perhaps it isn't?

Legislation to enable the northern leg of HS2 (Phase 2b) will go before Parliament in 2020, a year later than originally planned, The Times reports.

The government says the delay to the legal framework — reported to be related to yoking the HS2 proposals firmly to plans for transpennine Northern Powerhouse Rail — will not affect the timetable for the rail line itself.

The legislation was intended to be submitted in 2019, with approval due by 2022 to be ready for a start of construction work, itself due for completion by 2033.

The new plan is that the bill will go before Parliament in 2020, which means that either Parliament has less time, or the construction process must be quicker.

This is where the math (or the politics) gets confusing. Getting legislation through Parliament as quickly as the government envisages may not be easy, if the earlier phase of HS2 is any guide. Legislation authorising the London to Birmingham phase of HS2 was lodged in 2013 and did not receive Royal Assent until 2018, Construction News reports.

If the Phase 2b bill took as long to pass through Parliament then work on-site on the Midlands to Manchester section could not begin until 2025, pushing the completion of building works back to 2036. Unless, of course, construction work was three years ahead of schedule.