Editing M1 motorway (section)

===London extensions, 1966, 1967 and 1977===
{{unreferenced section|date=October 2017}}
[[File:M1 construction.png|upright=0.9|thumb|right|Map showing construction dates of sections of the M1]]
[[File:M1 Motorway, Junction 4 - geograph.org.uk - 85978.jpg|right|thumb|M1 at junction 4. The old overhead lane control gantries are still visible, which were replaced with newer, verge-mounted MS4 [[Variable-message sign|variable message signs]] in 2008.]]
The M1 was extended south towards London from its original starting point at junction 5, in three stages. The first stage, opened in 1966, took the motorway south-east, parallel to the [[A41 road|A41]], to meet the A5 at junction 4 south of [[Elstree]]. The second phase continued east to [[Scratchwood]] ([[London Gateway Service Area|London Gateway Services]], which occupies the location of the missing junction 3, from where an unbuilt spur would have connected to the A1 at Stirling Corner to the north-east). The M1 then runs south alongside the [[Midland Main Line]] towards [[Hendon]], where it meets the A1 again at junction 2 via a tightly curved flyover section. These flyovers connecting from the A1 were originally both for northbound traffic: the left one as the on-ramp to the M1, the right one going over the A1/A41 junction beneath to rejoin the A1 northbound.

Junction 2 is about {{convert|2.5|mi|km|0}} south of the original junction 3. Before the completion of junction 2, southbound traffic left the motorway via a slip road which passed around the back of the now disused Homebase and under the A41/A1 Mill Hill Bypass, and looped round to join it at Fiveways Interchange. This slip road is still visible to southbound traffic approximately {{convert|650|yd|m}} before junction 2, and was maintained until the early 2000s, even though not accessible to traffic. The northbound slip road from the A1 is now partially used as the entrance way to a retail park and was once carried by bridge, but no longer reaches the northbound carriageway, because it is cut off by the motorway continuing south.

The final section of the M1 was opened to junction 1 at [[Staples Corner]] in 1977. There the motorway meets the [[A406 road|North Circular Road]] (A406) at a [[grade separation|grade separated]] junction and roundabout. Unrealised plans from the 1960s would have seen the motorway continue through the junction on an elevated roadway to end at [[West Hampstead]], where it would have met the [[North Cross Route]], the northern section of the [[London Ringways#Ringway 1|London Motorway Box]], a proposed ring of urban motorway around the central area. The layout of the Staples Corner junction was originally built in accordance with those plans, although most of the [[London Ringways]] Plan had been cancelled by 1973. Around the same time, the section between the then-M10 and junction 5 was widened from the original two lanes to three.

On its completion, the M1 acted as a fast link road between London and [[Birmingham]] via the M6. It also provided a link to [[London Luton Airport]] for those regions, and its proximity to the site of the [[new town]] of [[Milton Keynes]] (designated in 1967) meant that it was soon providing a vital transport link to another major area.