We present the UV photometry of the old open cluster NGC188 obtained using images acquired with Ultraviolet Imaging Telescope (UVIT) on board the AstroSat satellite, in two far-UV (FUV) and one near-UV (NUV) filters. UVIT data is utilised in combination with optical photometric data to construct the optical and UV colour-magnitude diagrams (CMDs). In the FUV images, we detect only hot and bright blue straggler stars (BSSs), one hot subdwarf, and one white dwarf (WD) candidate. In the NUV images, we detect members up to a faintness limit of $\sim$22 mag including 21 BSSs, 2 yellow straggler stars (YSSs), and one WD candidate. This study presents the first NUV-optical CMDs, and are overlaid with updated BaSTIIAC isochrones and WD cooling sequence, which are found to fit well to the observed CMDs. We use spectral energy distribution (SED) fitting to estimate the effective temperatures, radii, and luminosities of the UV-bright stars. We find the cluster to have an HB population with three stars ($T_{\rm eff}=4750–21000$ K). We also detect two yellow straggler stars, with one of them with UV excess connected to its binarity and X-ray emission.

King 2, one of the oldest clusters in the Milky Way, with an age of $\sim$6 Gyr and distance of $\sim$5700 pc, has been observed with UVIT payload on the AstroSat. With membership information derived from Gaia EDR3, the cluster is found to have 39 blue straggler stars (BSSs). We created multi-wavelength spectra-energy distributions (SED) of all the BSSs. Out of 10 UV detected BSSs, 6 bright ones were fitted with double component SEDs and were found to have hotter companions with properties similar to extreme horizontal branch (EHB)/subdwarf B (sdB) stars, with a range in luminosity and temperature, suggesting a diversity among the hot companions. We suggest that at least 15% of BSSs in this cluster are formed via mass-transfer pathway. When we compared their properties to EHBs and hotter companions to BSS in open and globular clusters, we suggest that EHB/sdBs like companions can form in binaries of open clusters as young as 6 Gyr.