Why do ships sail under flags of convenience?

Questions over the seizure of oil tankers

The threat of military action between Britain and Iran over the seizure of oil tankers is provoking debate about a common shipping practice.

Many vessels are owned by companies in one country but registered in another.

One example is the Iranian tanker Grace 1, which was detained by Britain's Royal Marines a couple of weeks ago.

Like around 7,000 ships world-wide, the tanker is registered in Panama.

The Panamanians say they removed the supertanker from their shipping register two months ago.

Panama has deregistered around 60 ships in the past few months, most of them linked to Iran and Syria.

Are flags of convenience an inconvenient truth for the shipping industry?