British businesses are beginning to regard this summer's London Olympics as an economic opportunity, but many have yet to resolve how they would cope with an unexpected incident such as a security threat, a survey said Monday.

Security, transport and staff availability continued to be the biggest concerns among the 200 large businesses questioned in the latest Deloitte survey.

Bosses are beginning to plan ahead, including 55 percent who said they will install screens in offices for staff to catch up on their favourite sports rather than risk empty offices.

But preparing for a major incident remained far off for the vast majority.

A well-prepared 'UK plc' is a vital part of the success of this summer and it is encouraging to see so many companies taking the Games seriously, Heather Hancock, lead London 2012 partner at Deloitte, said in a statement.

Whilst the precise economic impact of the Games remains a topic of much debate, what is certain is that the best-prepared and most agile businesses will grab the biggest share of the upside.

The number of firms which had assessed the possible impact of the Games had nearly doubled on last year to 87 percent, with 81 percent anticipating an economic boost compared with a previous 38 percent.

An information campaign by Transport for London on how companies could cope with deliveries and getting staff to work on a congested system seemed to be working, with concerns about disruption falling to 32 percent from 35 percent last year.

Staff unavailability remained the biggest worry, at 42 percent, forcing companies to look at remedies such as a review of holiday policies, 43 percent, and flexible working, 33 percent.

Security was a growing concern, up four percentage points to 41 percent.

But only 20 percent were planning to review their business continuity measures, such as how they might respond to a cyber threat, terrorist attack, transport disruption or flooding.

Most business continuity plans are designed to deal with one-off incidents played out over a short period of time, said Rick Cudworth, lead partner for Games readiness at Deloitte.

With the Olympic Games, there is the potential for several continuity challenges to impact at the same time and for a prolonged period.

The report also urged British businesses to look ahead to future Olympic Games and international sporting events, to see how they might tap into Britain's Olympic legacy, offering their knowledge and expertise.

(Reporting by Avril Ormsby)