If the prime minister were to dissolve parliament before the vote, there would be a generalelection under the current, flawed system, delaying long-hoped-for political reform.
Obama would be the first major presidential candidate to drop out of the modern campaign financing system for the generalelection since its creation in 1976 in the post-Watergate era.
The opposition Conservatives say that if they win power at the approaching generalelection they will copy the Scottish system, in which people who are not convicted usually have their DNA removed from the database as soon as the case against them is dropped.