The Ministry of Defence spent £149 million on an "urgent" upgrade to 900 tanks that are now only being used in training exercises, it was revealed.

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The tanks were upgraded for use in Iraq but are unsuitable for deployment in Afghanistan where Mastiff and Ridgback vehicles are better suited to cope with the terrain and threat.

The refit programme, ordered as an "urgent operational requirement" three years ago, saw 900 FV430 variant vehicles given new engines, drive trains and driver controls and reclassified as Bulldogs.

An MoD spokeswoman said: "We provide our Armed Forces with the vehicles that best meet their operational need.

"The Bulldog was specifically upgraded for use in Iraq where it played a key role in providing armoured protection for many personnel.

"In Afghanistan, where the terrain and threats are different, this role is performed by the Mastiff and Ridgback.

"The Bulldogs continue to have a role in training exercises in the UK."

The upgrade came to light after freedom of information requests submitted by The Times newspaper.

The Mastiff and the Ridgback, it's "baby brother", were rolled out in Afghanistan to withstand the increasing threat of roadside bombs and take the place of the more vulnerable Snatch Land Rovers.