The defence secretary has revealed that an extra 400 British troops are to be sent to Iraq to support the election process.

But the move provoked fury among MPs who claimed Geoff Hoon had "slipped out" the announcement during a session of defence questions on Monday.

As the Commons returned from its Christmas recess, Hoon used the session to announce the First Battalion the Royal Highland Fusiliers will be dispatched to the UK-controlled southern zone of Iraq "for a limited period of time in support of election security".

The "extremely high readiness troops" are currently based in Cyprus and will be moving shortly to support the ballot on 30 January.

With violence escalating in the run-up to the poll the Iraqi authorities have called for extra help from the US and UK and Hoon said the decision was made on the basis of military advice.

However the decision to make the announcement during question time, rather than in a full oral statement to the House as is usually the case, triggered an angry response from both major opposition parties.

Conservative chief whip David Maclean said the tactic was "outrageous" while senior backbencher Sir Patrick Cormack claimed it broke with convention.

Hoon insisted the claims were "nonsense" and that it was legitimate to use the question time to update the Commons on the latest developments.

He said he did not wait until the end of the session because he wanted to "take the earliest opportunity" to inform MPs.

On the operational move he added there are no more plans to deploy British troops outside of the UK zone, as some reports have suggested.

But Tory defence spokesman Keith Simpson said the need to send more soldiers showed the requirement for "more infantry, not the cuts that he has carried out".

Hoon said the deployment had "no relevance whatsoever" on the "adjustments" to the army announced before Christmas.