Harrier gun
The question of why the **** don't we fit a 30mm Aden - or even an off the shelf pylon mounted gunpod ( with relevant quite simple test range trials, & if one wants to be fussy a bit of new weapon aiming HUD software too ) has been asked long ago, and no doubt continues to be so ' in theatre ' !
Put the aircraft name into a search engine, select 'history' then scroll down to 'Harrier Testing'.
I suppose rockets ( and we were openly told the UK had an embarassingly large stockpile soon to time-expire ) look impressive to politicians...