Thank you John. I now have feeling it is a Sony E6-30HMEX tape, but not 100% sure. I've posted a query on their site, which says the current equivalent has a clear leader.
The photo was taken by UK Navy accident investigators after the wreckage was recovered from the Arabian Gulf after a mid-air in 2004, 3 days after the invasion. The tape had been immersed in salt water for 3 weeks as recovery was too dangerous. The outer reels were badly damaged. About the last 10 minutes of video are missing, 1 minute of audio. The unit is "sealed" in the sense it is splash proof, the main concern being hydraulic oil and salt water. It is not a crash proof accident data recorder ("black box"), but a mission recorder, designed to be pulled out by the observer when they land. It contains the only recorded data of the crash (officially that is, as the US refused to release their recordings). This is the only image, as it happens to be the only one in the investigator's report. The UK won't release any more information.
I'm afraid there wasn't much care taken by the original investigator, who just took it out and stuck it in a Hi8 machine. It was only many months later that the cassette was sent to specialists in New York and a different interpretation of what was said emerged. Many thanks again.