"If the merchant vessel was located where the British Ministry of Defence claims (29° 50.36'N, 48° 43.08'E), the incident appears to have taken place on what is technically land territory rather than in the territorial sea. More importantly, the point is clearly south of both the 1975 boundary and the median line between the two low-water lines.
Both of the positions that the Ministry of Defence stated were supplied by the Iranian government lie just seaward of the land boundary terminus. The position that was initially reported (29° 51'N, 48° 45.11'E) is 0.5 nautical miles south of the median line; ..."

As I said, the parties agreed initially it was in Iraqi territory. SOUTH is in Iraq, NORTH is in Iran, according to the map.

And as I said, EVEN if the Brits had been over the line, the Iranians DID NOT have the right to capture them.