Met explosive officers swooped on the M40, north west of London, after a number of "items" were found.
The unidentified items were found by members of the public on Wednesday.
Police were called to the area between junction three and four of the eastbound carriageway of the motorway.
A met spokesman said the officers were called to the scene - between Handycross and Loudwater - as a "precautionary measure".
Forensic officers returned this morning to continue the investigation and remain at the scene.
As a precautionary measure one lane of the motorway travelling eastbound was closed by officers causing huge tailbacks.
Police are not speculating as to whether this investigation is linked to the terrorist investigations going on in High Wycombe.
Police said the items had not been removed and would not release any further information.
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