The HS2 route to Crewe has been labelled "unachievable" by an official watchdog.

The Infrastructure and Projects Authority (IPA) has given a "red" warning for the first two phases, which will see the line travel from London to Birmingham and then onto Crewe.

Both phases of the high speed rail link have faced significant delays and the review said the whole project may need to be "reassessed".

Estimates say the project has increased in costs from £33 billion in 2010 to at least £71 billion, but the UK Government says it is still committed to the project.

The IPA report into major projects across the country said: "Successful delivery of the project appears to be unachievable.

"There are major issues with project definition, schedule, budget, quality and/or benefits delivery, which at this stage do not appear to be manageable or resolvable.

"The project may need re-scoping and/or its overall viability reassessed."

Transport Secretary Mark Harper visited the Birmingham section of the line earlier this month with his Australian counterpart, Catherine King, to see the construction of HS2's new Curzon Street station.

The Department for Transport said the visit "marks [the] Government's ongoing commitment to the high-speed line".

In March, Nub News reported the government confirmed the HS2 line between Birmingham and Crewe was to be delayed by two years.

In a written statement, Mr Harper said: "The government remains fully committed to delivering HS2 from Euston to Manchester.

"However, in recognition of inflationary pressures and to help balance the nation's books, the next two years will be used to re-phase construction and optimise future delivery of Phase 2a between Birmingham and Crewe so this is done in the most cost-effective way.

"This aims to deliver high-speed services to Crewe and the North West as soon as possible after accounting for the rephasing of construction."