Direct proof of use
A UK Ministry of Defence answer to Parliament, answered on 29 January 2019, states that the Royal Saudi Air Force operated UK-supplied Typhoon and Tornado aircraft in Yemen and used Storm Shadow munitions there.
A UK parliamentary evidence submission to the Committees on Arms Export Controls inquiry also records that Royal Saudi Air Force Typhoon and Tornado aircraft were deployed on combat missions in the Yemen campaign and that small numbers of UK-sourced Storm Shadow missiles were used.
Sources: Military Intervention - Written Question 210522, UKY0013 - Evidence on Use of UK-Manufactured Arms in Yemen
Timeline
Saudi Arabia began coalition military intervention in Yemen on 26 March 2015 after President Abdrabbuh Mansur Hadi requested assistance against Houthi-aligned forces. The Storm Shadow evidence does not identify individual strike locations or targets, but it places the missile in Royal Saudi Air Force use during that Yemen campaign.
The clearest public confirmation came in January 2019, when the Ministry of Defence listed Storm Shadow among UK-supplied munitions used by Saudi Arabia in Yemen since March 2015.
Sources: UKY0013 - Evidence on Use of UK-Manufactured Arms in Yemen, Military Intervention - Written Question 210522
Narrative
Storm Shadow appeared in the Yemen war as a Saudi-operated, UK-supplied air-launched cruise missile rather than as a Yemeni government weapon. The documented operator was the Royal Saudi Air Force, which used UK-supplied aircraft and precision-guided munitions during the Saudi-led coalition air campaign.
MBDA describes Storm Shadow/SCALP as an air-launched, conventionally armed long-range deep-strike weapon for pre-planned attacks against high-value fixed or stationary targets. In the Yemen record, the public evidence supports the broader role of air-launched precision strike, but it does not publicly identify the exact Saudi sorties, target sets, launch aircraft, or number of Storm Shadow missiles fired.
Sources: Military Intervention - Written Question 210522, UKY0013 - Evidence on Use of UK-Manufactured Arms in Yemen, STORM SHADOW / SCALP