They specialize in land-based construction as well as environmental and support services.

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Halliburton consists of two major divisions, KBR, which provides logistics and construction services, and the Energy Services Group, which concentrates on support services for oil explorers.

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Carillion, which was spun out of Tarmac as a pure construction company in 1999, now makes two-thirds of its operating profit from support services and PFI investment.

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Balfour Beatty became known as a construction firm but now calls itself an infrastructure company, investing in transport systems and providing professional and support services in many markets including America, Hong Kong and the Middle East.

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But, as attention has focused on accounting standards, concerns have been raised in particular about how support services firms treat the large costs run up bidding for public private partnership contracts, such as hospital construction projects.

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