LONDON (Reuters) - A potential lack of available staff and the risk of a security incident are British business' biggest concerns during next year's London Olympics, a survey showed on Saturday.

The latest "Games Readiness" survey by business advisory firm Deloitte showed that a growing number of companies had begun to evaluate how the Games might affect them, but the majority had yet to assess the situation.

Among those who had, disruption on London's creaking transport system and a potential lack of hotels also featured highly.

"UK businesses are waking up to the fact that if they want to capitalize on any business boost from the Games, as well as minimize disruption to their company, they need to prepare and be ready," Heather Hancock, lead London 2012 partner at Deloitte, said in a statement.

"However, there is much work to be done, and it is a concern that over half of large UK businesses have yet to formally assess the impact the Games could have on their operations."

About 300 companies, with more than 500 staff, were questioned for the survey, two-thirds of them in London.

About 42 percent of them said they had examined the opportunities and challenges facing their businesses, up from 15 percent last year. Just 5 percent believed there was no need for such an assessment, compared with 56 percent in 2010.

More than half, 55 percent, think their preparations are on track.

Concern about a potential lack of staff was the biggest worry, 43 percent compared with 23 percent last year, while fear of security risks had gone up to 37 percent from 5.5 percent.

Transport has consistently been a worry, with about a third citing it.

Another concern was the number of senior staff planning to take a holiday during the Games, with executives from tourism, hospitality and leisure companies, at 29 percent, the most likely to jet away.

(Reporting by Avril Ormsby)