Train services suffered huge delays on Wednesday after a trolley was left on the lines near Bleak Hall.
A London Midland train struck the trolley at 5.30pm and was unable to continue its journey.
Two other services were cancelled as a result of the incident, and 65 others were delayed, amounting to a total of nine hours of delays.
Inspector Neil Ketley, based at Milton Keynes Central station, said: “We received reports of stones being thrown at two train services, smashing windows before a trolley was thrown onto the tracks from a bridge between Milton Keynes Central and Bletchley.
“These tracks form part of the line into London and the damage to the train caused serious delays across the region and on the West Coast Mainline.
“I simply cannot overstate how dangerous these actions were. It is sheer luck that the incident was not more serious but we may not be so fortunate if this happens again.
“Trains on this line travel at high speeds and there is a very real risk when they strike objects on the track that they could be derailed. Had this happened on this occasion the results could have been catastrophic. Endangering safety on the railway with intent carries a sentence of up to life imprisonment.
“It’s hard to believe anyone could take pleasure or excitement from such a reckless act and it is vital that we identify those responsible.
“If you were in the area at the time and saw anything suspicious, or know who might have been responsible, please get in touch.”
Simon Whitehorn, Network Rail general manager, said: “This reckless behaviour is unacceptable and those responsible are fortunate that the impact of their actions was not more serious. Network Rail fully supports British Transport Police’s attempts to track down these criminals so they can face the consequences of their irresponsible actions.”
Anyone with information about the incident should contact BTP on Freefone 0800 40 50 40 quoting reference B8/LNA of 23/08/2012. Alternatively, contact the independent charity Crimestoppers anonymously on 0800 555 111.