GPS Data Will Prove Brits Were Not In Iranian Waters

I was wondering when GPS data would be made available in the kidnapping of the British sailors:

The British foreign secretary is expected to explain to MPs the global positioning system co-ordinates of the 15 servicemen to prove they were well inside Iraqi waters in the Shatt al-Arab waterway.

What I wonder is if they still have a way to track these guys? Special tags in their clothing or something like that? That would sure make the rescue effort easier.