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Location Map ( geo)
Cameraicon.png View gallery (40)
From:  Brackley (SP577334)
To:  Black Cat Roundabout, Roxton (TL159553)
Via:  Milton Keynes
Distance:  44.4 miles (71.5 km)
Meets:  A43, B4031, A4421, A413, B4033, B4034, A5, A4146, A5130, M1, A507, A428, B531, B530, A6, A600, A603, A4280, A1
Former Number(s):  B4031, B4034, B557, A428
Old route now:  A34, A41, A4421
Highway Authorities

Highways England • Buckinghamshire • Central Bedfordshire • Milton Keynes • Northamptonshire • Oxfordshire

Traditional Counties

Bedfordshire • Buckinghamshire • Northamptonshire • Oxfordshire

Route outline (key)
A421 Weston-on-the-Green - Finmere
A421 Brackley - Black Cat Roundabout


The A421 could be seen as having fallen on hard times, as it has now lost a good few miles of its original route, although in compensation it has been greatly extended at its eastern end.

Brackley - Black Cat

The new route now starts at the Barley Mow roundabout on the A43, just south of Brackley. This road was the B4030 but has now assumed a more important guise. From here the road makes the short journey to Finmere where it meets its old route. The road generally follows the B4030 route except for a new section just to the south-west of Mixbury and for the final part before meeting the A4421 at the Finmere Airfield roundabout.

Approaching Buckingham

Finmere and its neighbour Tingewick have now been bypassed with a high quality dual carriageway in part, somewhat out of place in my opinion. Quickly we arrive at the western end of the Buckingham bypass and traverse this by five roundabout junctions, including one with the A413 with which the road multiplexes for one section. The road then follows a new alignment for around 500 metres before joining the old route of the B4034. Originally, Buckingham (and the A413) marked the eastern end of the A421.

After the roundabout with the B4033 from Winslow. The road has been largely improved to a good standard, and we start to cross Whaddon Chase. As the road approaches Tattenhoe and Far Bletchley, the original B4034 takes the route to Bletchley, whilst the A421 adopts the guise of H8 (Standing Way). We cross the A5 without a junction (a spur leads off to a GSJ on the A5 from the next roundabout) and head through the outskirts of Milton Keynes towards the M1, crossing it via junction 13. This section is dualled up until the John Lewis Distribution centre just after the roundabout with the A5130.

The final stretch runs from junction 13 of the M1 to the Black Cat roundabout on the A1. As such it is a potentially important trunk route linking the A1 and M1. Moreover a little further north on the A1 is the A428 which joins up with the A14. This could therefore form a continuous route from the East-Anglian Ports to the South Midlands and also form a relief road to the M25.

The M1/A421 interchange has been updated, completed in 2012, to cope with a higher volume of traffic, and encourage the use of routes such as the A507, which now also has access to the M1 from that junction.

The road was also dualled between the M1 and Bedford bypass, where there are several large distribution centres.

Construction of the Great Barford Bypass

The bypass was opened in the late 1990s and goes round the south of the town. It is dual-carriageway throughout and there is a motorway-style junction with the A6. Shortly after this the only significant landmarks on the road come into view. These are the massive hangers that were built in the 1930s to house airships.

After the Bedford bypass we're on the new Great Barford Bypass, which runs from Bedford to the Black Cat which can hold its own horrors depending on the traffic on the A1.


The original start of the A421 on what was then the A43

Originally, the road started at the current A34 and B430 junction at Weston-on-the-Green. Back then this was a simple fork, which later became a roundabout, with the single-carriageway A43 from Oxford to Northampton. From here the road runs virtually straight towards Bicester, passing Wendlebury on its way and arriving into Bicester from the south. Through Bicester it became a slow moving road through the town, meeting the A41 (now B4100) in the centre. It then escaped north under the Marylebone–Banbury railway line and out towards Newton Purcell. The road becomes quite wide here due to an age-old improvement. It then dived under the now-disused Great Central Railway at Finmere Station. The road, still following a straight course, arrived at Finmere, site of a huge market on the old airfield.

The old route has now changed, dramatically in some places. From Weston on the Green the road is now the dual carriageway A34 link to the M40. From there it is dualled all the way to the Bicester bypass and is part of the re-routed A41. Indeed, the A421 south of Bicester had become a spur of the A43 by the mid-1940s but regained the A421 number in the 1960s. North of Bicester the road has been imaginatively renumbered the A4421.


The A421 from Oxford to the Black Cat forms part of the Oxford to Cambridge Expressway strategic study, for which an interim report was published in August 2016.



BBC News

JunctionsAshland Roundabout • Barleymow Roundabout • Black Cat Roundabout • Bleak Hall Roundabout • Bottledump Roundabout • Brinklow Roundabout • Cardington Cross • Coffee Hall Roundabout • Eagle Farm Roundabout • Elfield Park Roundabout • Elstow Interchange • Emerson Roundabout • Fen Farm Roundabout • Harrowden Interchange • Hospital Roundabout (Milton Keynes) • Kents Hill Roundabout • Kingston Roundabout • Marina Roundabout • Marsh Leys Roundabout • Marston Junction • Netherfield Roundabout • Redmoor Roundabout • Renhold Interchange • Ridgmont Interchange • Rodney House Roundabout • Simpson Roundabout • Tattenhoe Roundabout • Tesco Roundabout (Buckingham) • Windmill Hill Roundabout
CrossingsBedford Bypass Viaduct
RoadsH8 (Milton Keynes) • V6 (Milton Keynes)
PlacesBedford • Bicester • Buckingham • Milton Keynes • St Neots
Related Pictures
View gallery (40)
421 - Half open - Coppermine - 12839.jpgA421 - Old road layby - Coppermine - 12841.jpgA421 Great Barford Bypass - Coppermine - 9022.jpgBourton roundabout from A421 (C) John Firth - Geograph - 3152779.jpgStanding Way approaching Trafalgar... (C) John Firth - Geograph - 3675907.jpg
Other nearby roads
BicesterA34 • A4095 • A41 • A43 • A4421 • Akeman Street • B4011 • B4029 (Oxfordshire) • B4030 • B4100 (Bicester - Bishops Tachbrook) • E05 • Longest Lane • M40 • NCN51 • T35 (Britain)
BuckinghamA413 • A422 • A4421 • B4031 • B4034 • C137 (Buckinghamshire) • C15 (Buckinghamshire) • C18 (Buckinghamshire) • C3 (Buckinghamshire) • C51 (Buckinghamshire)
Milton KeynesA4146 • A422 • A5 • A50 • A506 (Hockliffe - Northampton) • A508 • A509 • A5130 • B4033 • B4034 • B488 • B526 • B557 • C129 (Milton Keynes) • C130 (Milton Keynes) • C131 (Milton Keynes) • C132 (Milton Keynes) • C13 (Milton Keynes) • C140 (Milton Keynes) • C141 (Milton Keynes) • C142 (Milton Keynes) • C143 (Milton Keynes) • C144 (Milton Keynes) • C145 (Milton Keynes) • C146 (Milton Keynes) • C147 (Milton Keynes) • C149 (Milton Keynes) • C150 (Milton Keynes) • C151 (Milton Keynes) • C152 (Milton Keynes) • C154 (Milton Keynes) • C155 (Milton Keynes) • C156 (Milton Keynes) • C157 (Milton Keynes) • C158 (Milton Keynes) • C159 (Milton Keynes) • C160 (Milton Keynes) • C162 (Milton Keynes) • C179 (Milton Keynes) • C181 (Milton Keynes) • C24 (Milton Keynes) • C41 (Milton Keynes) • C5 (Milton Keynes) • C9 (Milton Keynes) • E13 • E31 (via Carlisle) • E33 (London - Glasgow) • H10 (Milton Keynes) • H1 (Milton Keynes) • H2 (Milton Keynes) • H3 (Milton Keynes) • H4 (Milton Keynes) • H5 (Milton Keynes) • H6 (Milton Keynes) • H7 (Milton Keynes) • H8 (Milton Keynes) • H9 (Milton Keynes) • Holyhead Road • M1 • NCN51 • T11 (Britain) • V10 (Milton Keynes) • V11 (Milton Keynes) • V12 (Milton Keynes) • V1 (Milton Keynes) • V2 (Milton Keynes) • V3 (Milton Keynes) • V4 (Milton Keynes) • V5 (Milton Keynes) • V6 (Milton Keynes) • V7 (Milton Keynes) • V8 (Milton Keynes) • V9 (Milton Keynes) • Watling Street
BedfordA418 • A422 • A428 • A4280 • A5134 • A5140 • A5141 • A6 • A600 • A6002 (Bedfordshire) • A603 • A6172 (Bedford) • B530 • B531 • B5379 • B557 • B560 • B561 • B562 • B563 • B564 • B659 (Bedford) • B660 • C94 (Bedford) • E24 • E28 (Birmingham - Ipswich) • NCN51 • T12 (Britain) • T45 (Britain)
St NeotsA1020 (St Neots) • A428 • A45 • B1041 • B1043 • B1046 • B1048 • B1428 • B645 • C171 (Cambridgeshire) • C174 (Cambridgeshire) • E112 (Old System) • E24 • E28 (Birmingham - Ipswich) • E31 (via Newcastle) • M100 • NCN51 • T1 (Britain) • T45 (Britain)
A400 • A401 • A402 • A403 • A404 • A405 • A406 • A407 • A408 • A409 • A410 • A411 • A412 • A413 • A414 • A415 • A416 • A417 • A418 • A419
A420 • A421 • A422 • A423 • A424 • A425 • A426 • A427 • A428 • A429 • A430 • A431 • A432 • A433 • A434 • A435 • A436 • A437 • A438 • A439
A440 • A441 • A442 • A443 • A444 • A445 • A446 • A447 • A448 • A449 • A450 • A451 • A452 • A453 • A454 • A455 • A456 • A457 • A458 • A459
A460 • A461 • A462 • A463 • A464 • A465 • A466 • A467 • A468 • A469 • A470 • A471 • A472 • A473 • A474 • A475 • A476 • A477 • A478 • A479(W) • A479(E)
A480 • A481 • A482 • A483 • A484 • A485 • A486 • A487 • A488 • A489 • A490 • A491 • A492 • A493 • A494 • A495 • A496 • A497 • A498 • A499
Defunct Itineraries & Motorways: A403 • A404(M) • A405 • A407 • A423(M) • A430 • A437 • A446(M) • A455 • A464 • A475 • A491