A final decision on whether to go ahead with the controversial HS2 high-speed rail line between London and Birmingham is being delayed until the New Year, it has been disclosed.

Transport Secretary Justine Greening is understood to be considering whether a £500 million tunnel should be bored to minimise impact on the Chiltern Hills landscape.

The 100-mile rail link, due to be built between 2016 and 2026, aims to cut the London-to-Birmingham journey time to 49 minutes.

However, the £32 billion project has provoked fury among many Tory MPs - including Welsh Secretary Cheryl Gillan, who has reportedly threatened to resign over the issue.

Ms Greening had been expected to make a final announcement before parliament rises for its Christmas break.

But the decision has now been delayed until January as she has asked for a feasibility study to be carried out on a £1.5 million tunnel near Amersham, as well as an environmental probe.

The money would come from within the existing budget, as savings have been identified from other parts of the route.