[7] The upgrade work for this final phase of the plan, the section running from junction 13 to Eagle Farm roundabout, started in September 2018 and was completed in December 2020.

The case for its creation was examined in a Strategic Study for the Cambridge – Milton Keynes – Oxford corridor, published by National Infrastructure Commission in November 2016.

[11] The NIC saw the road as being of national strategic importance by providing an outer orbital route around London, linking Southampton, the M3, M4, M40, M1, A1, A14/M11 and Felixstowe.

In March 2021, Transport Secretary Grant Shapps cancelled the plan, citing analysis that showed that its costs would exceed its benefits.

[12] The A421 Tingewick bypass has a minor claim to fame as the location of the then fastest speeding incident ever recorded by British police, in March 2003.

[13] Andrew Osborne, 31, of Leamington Spa, was filmed by a mobile speed camera while travelling at 157 miles per hour (253 km/h) on a motorcycle.

[13] Blind Martine Brooks drove along the newly constructed A421 Great Barford Bypass (From the A1 Black Cat roundabout to Bedford) and back to raise money for charity.