You may already have all this information but from the excellent "Fleet Air Arm Helicopters Since 1943" book by Lee Howard, Mick Burrow and Eric Myall:
ZG875. During rotors-running refuel on deck, uncontrolled yaw to port, spun around stbd sponson which collapsed, a/c fell on starboard side, onboard Spanish Navy frigate SNS Reina Sofia in Eastern Minch, Scotland, Cat. 4, 12.6.99 (Lt AC Chaloner, Lt JR Mitchell & Lt M Roberts OK, L/A A Davies injured); Offloaded Faslane 14.6.99; FSAIC Yeovilton by road 17.6.99; 760 Sqdn/DCAE Sultan, Gosport by road 30.10.00 as GI Class GR(2) A2816; Extant [TFH 3700.35]
Abbreviations Decode: Cat. - Category of Accident. L/A - Leading Airman. FSAIC - Flight Safety and Accident Investigation Centre. DCAE - Defence College of Aeronautical Engineering. GI - Ground Instructional (Airframe). TFH - Total Flying Hours.
There are two M Roberts in the Fleet Air Arm Officers' Association - Chaloner and Mitchell are not listed as members. An enquiry to the Administration Director, FAAOA, 4 St James's Square, London, SW1Y 4JU may be beneficial as that may result in your request being placed on the website. There must be quite a few 820 aircrew of that era as members who will know more.