The real reason why the Iranians seized the British ships? According to London’s Al-Sharq Al-Awsat, it was all an ingenious plan. From MEMRI (with thanks to Romy):
“A source close to the [Iranian] Revolutionary Guards told Al-Sharq Al-Awsat of the real reasons and factors in the apprehension of the three British Navy vessels and the arrest of the sailors by Iranian Coast Guard patrol forces on Monday [June 21, 2004]. He indicated that the British Army command in Iraq had understood the message sent them by the Iranian Revolutionary Guards command by their capture of the ships.”
‘Detention of 40 Volunteers for Suicide Operations Was Great Concern to the Revolutionary Guards’
“According to the source, the content of the message was very simple: ‘Release our comrades, whom you are holding, and we will release your soldiers.’ The source clarified that the detention of 40 volunteers for suicide operations by the Ukrainian forces acting in Iraq was of great concern to the Revolutionary Guards command, because they [the 40] constituted the first group of volunteers participating in the Organization for the Commemoration of the Shahids, which was established recently by Revolutionary Guards Commander Col. Dhu al-Qadr.
“Al-Sharq Al-Awsat was informed that one of the senior leaders of the Revolutionary Guards, who had formerly held the post of head of the Committee for Iran-Ukraine Military Cooperation, had gone to Kiev for talks regarding the Iranian detainees. However, it turned out that the Ukrainian units had already handed the volunteers for suicide operations over to British forces acting in southern Iraq.
“Despite contacts between the Iranian and British military committees at the borders and daily contact between them in small conflict resolution – [such that] this has become routine since the British forces entered southern Iraq – the British command has so far refused to acknowledge that it is holding 40 Iranian volunteers in one of its detention camps. According to the Iranian source, this caused the Revolutionary Guards leadership to seek a semi-military solution to bring its men back from Iraq.”