The original HS125s operated by 32 Squadron 'A' Flight were civvy aircraft, leased in from Hawker Siddeley, which is perhaps why they weren't named.
On the other hand, the HS748 Series 2A aircraft operated by 'B' flight and VIP flights in overseas commands, being owned by the RAF, were named after the Andover that was loosely based on the HS748 design.