Remember how the airspace was closed because of predictions from computer models of the movement of volcanic ash particles that would wreck jet engines? The UK's Met Office was responsible for the North Atlantic and the NERC handled the operation of a twin-turboprop Dornier 228 capable of sampling up to 20,000 feet and a LIDAR-equipped BAe 146 four-engined short-haul jet that could reach 31,000 ft to take actual measurements. Unfortunately at the critical time, the BAe 146 was having a paintjob and had to be rushed out of the hangar...
However, back in 1983 the RAF ordered four VC-10 K.3 tankers, the last three of which (ZA148-150) had provision for air sampling pods (believed to be converted Sea Vixen drop tanks) to be fitted under the wing*. This was because the Vulcan B.2MRRs of 27 Squadron which hitherto performed this role were being retired and the squadron disbanded. In 2006 two VC-10 K.3s fitted with the pods flew to Japan to monitor the North Korean nuclear test. And again in 2009 according to the Times and PPRuNE.
It beggars belief that an aircraft with the transatlantic range (5,855 nautical miles without air-to-air-refuelling) and 38,000 ft service ceiling of the VC-10 was not used to gather data on the ash to confirm the computer model predictions. Flying could have been resumed earlier as aircraft could have diverted around the dispersed ash plumes. I googled ZA148, ZA149 and ZA150 and found plenty of lovely photos of all three aircraft flying before and after the imposition of the Atlantic NFZ.
Were all three aircraft unserviceable or otherwise engaged at the time?
* Either on the fifth (spare) engine attachment close to the starboard wing root or (more likely) in place of the outer wing hose drum refueling units.