These types of files can be matched using the household identifiers, w_hidp. So, if you want to merge the individual level file a_indresp and the household level file a_hhresp use a_hidp. Similarly, if you want to merge d_indresp and d_hhresp use d_hidp. But as the household identifier is only unique for each household within a wave, it cannot be used to match individual and household level files from different waves. So, you cannot match a_indresp and d_hhresp files. [Note, w_ is the wave prefix placeholder which is equal to a for Wave 1, b for Wave 2 and so on.]
The syntax for matching individual and household level files from the same wave is available here (see under the UKHLS deposited tab and title “Distributing household level information to the individual level”).
