The 2nd Battalion Princess of Wales' Royal Regiment is to be sent to Iraq to replace 40 Commando Royal Marines, the armed forces minister has announced.
40 Commando will complete a six-month deployment in January.
The deployment was part of routine troop rotation, Adam Ingram said.
The total number of UK personnel in Iraq - about 9,000 - would be broadly unchanged by the January deployment.
Around 550 troops of 40 Commando are currently based near Basra, with another 50 serving with the Black Watch at Camp Dogwood near Baghdad.
The Ministry of Defence said the Aldershot-based battalion of the Princess of Wales' Royal Regiment, known as the Tigers, would make the move in early January, when the 40 Commando finishes its six-month deployment.
In a further shuffle, the 1st Battalion the Royal Scots will become the Very High Readiness Reserve, on 10 days' notice to deploy to Iraq.
"These are routine adjustments to UK forces in [the area near Basra]," Mr Ingram said.
The multinational force was continuing to reconsider troop levels required in the run-up to Iraqi elections in January 2005.
"If we judge that further changes to the UK military contribution in Iraq would be appropriate to support this process we will of course inform the House at the earliest opportunity," Mr Ingram said.
"At present, however, no such decision has been made," he added.