Back in 2009, I argued in favour of republicanism on Liberal Democrat Voice (was a non-party member at the time);
The current head of state is a lame duck. If Her Majesty – at the demand of The Sun – dissolved Parliament and dismissed her government over the expenses scandal, the Crown would be instantly attacked (and removed) via the governing party. Any Royal power would be seen as a provocative act towards Parliament (the Royal veto was last used in 1708). A Presidential system could solve many constitutional problems because, significantly, the President would have a democratic mandate to rule with authority and be political. Liberals may have led the way on electoral and House of Lords reform, but our voice is needed to justify the removal of the Crown. Britain, and her future, is better off under the administration of a republic.
The Liberal Democrats have a political duty to argue against the Crown. Monarchists will, inevitability, deny us the right to question the Crown and propose a counter-system. But we cannot steer away from the debate. A monarchist once asked me to choose between President Blair or President Thatcher, but the beauty is, as I said, both can be voted out of office. Queen Elizabeth cannot.