Everything that is live naturally creates earth leakage even under normal operating conditions. One metre of twin and earth generates a tiny amount of capacitive leakage from line to CPC; 100 metres creates 100 times as much. All the wiring in a house might create a milliamp or two, appliances somewhere between 0.1mA and 3mA each, etc. Normally this is of no account but as soon as the CPC is disconnected, all the tiny leakages downstream of the disconnection point will raise the voltage of the disconnected CPC and everything fed from it, until the current leaking out of the CPC equals the amount leaking in.
What voltage actually appears depends on the potential divider formed by a) the total parallel leakage impedance from line to the disconnected CPC and b) the total parallel leakage impedance from the disconnected CPC to true earth. Anywhere between zero and 230V to true earth is possible, but voltages of 50-150 seem most common on disconnected CPCs. Because the impedances of the leakage paths are high, measuring the voltage with a meter often changes it drastically - making it an example of a so-called 'ghost voltage.'
BTW, 'voltage through it' is not the best choice of terminology. Voltages appear 'between' two points. Currents flow 'through' a conductor.
