The 284 miles (457 km) A30 road from London to Land's End, used to provide the most direct route from London to the south west; more recently the M3 motorway and A303 road performs this function for much of the route and only parts of A30 now retain trunk road status. Places on the trunk section have been bypassed and sections of road widened.

This section of the A30 passes through many towns and villages, including Staines-upon-Thames, Camberley, Basingstoke, Salisbury, Shaftesbury, Sherborne, Yeovil and Honiton.

Much through traffic from the London area to south west England now uses the M3 motorway as far as Basingstoke then the A303 to Honiton where the route again joins the A30.

Between Basingstoke and Honiton, the A30 does not have trunk road status (except for short stretches around Salisbury, Shaftesbury and Yeovil) and is mostly single carriageway carrying local traffic.

This section is a major trunk road as far as Penzance, it is mostly dual carriageway; however there are several short sections of single carriageway.