Vanadium dioxide (VO2) is attractive for a variety of applications in optics and electronics, due to its abrupt insulator-metal transition (IMT) with > 103× change in resistance near room temperature. Use of VO2 in devices will require low power switching, with knowledge of the transition mechanism and behaviour down to nanoscale dimensions. To address this challenge, we use metallic carbon nanotubes (CNTs) with diameter 1 nm  to probe nanoscale IMT in VO2 for the first time. We find that a single CNT locally switches the VO2 at less than half the voltage and power otherwise required. Furthermore, to understand the nanoscale IMT we use scanning probe microscopy (SPM) techniques to study devices during operation.