Crossrail will cost about £5.5bn
Major building projects such as Crossrail and those linked to the 2012 Olympics could be delayed or cancelled because of rising costs, a report said.
Raw materials and labour costs have risen by 12% in the last year, the Royal Institution of Chartered Surveyors (Rics) study showed.
It said rising fuel and cement costs were having a dramatic effect on civil engineering projects.
Other affected projects could include Thameslink and the East London Line.
The £16bn Crossrail scheme, which will link Maidenhead in Berkshire to Shenfield in Essex, via central London, is due to be completed in 2017.
More than £5.5bn of government money is being put behind the venture.
The £5.5bn Thameslink project which will modernise the rail service and Transport for London speding £1bn to expand the East London Line from Whitechapel north to Highbury & Islington, and south to Crystal Palace and West Croydon.
Overall, with infrastructure output predicted to rise by 9% in 2008 and 7% in 2009, the industry is "well placed" to ride out the current economic downturn, said Joe Martin from the Rics.
"However, the industry is facing the possibility of a serious threat, caused by a combination of rising costs and the economic downturn, that could result in delays and, at worst, cancellation of some of these schemes," he said.