Where would we be without the M6? Nowhere at all. It's Britain's longest motorway and carries (in total, over its whole length) more traffic than any other. Part of it was also Britain's first.
The first motorway in Britain was the Preston Bypass, which was then incorporated into the M6 when construction was continued. Today it's found between junction 29 and M55 junction 1. The M6 contains all kinds of ground-breaking sections: the section along the Lake District has won awards for enhancing the landscape, for example. In a more mundane area and the section between Shap and Tebay is the only one in Britain to have an unconnected local road running down the central reservation.
Opened in 2003, the M6 Toll bypasses Birmingham, and is Britain's first toll road. Recently completed is the A74 upgrade, which extended the M6 right up to the border, connecting to the A74(M). The A74(M) and M74 were, when they were built, going to be renumbered as M6, creating a motorway over 350 miles long linking the M1 (and thus London) to Glasgow. That looks highly unlikely now.
However, the fact that the link between the two motorways was made at all is a cause for celebration, and it's fitting that it was on 5 December 2008 that the a new section opened - the fiftieth anniversary of the opening of the Preston Bypass.