London's small-and-medium sized companies (SMEs) could be in danger of underestimating the impact of next summer's Olympics on their businesses, which could limit sales as well as cause supply troubles for larger firms, a survey said on Monday.

About 55 percent of the 51 London SMEs questioned this summer predicted the Games would have no impact on their operations, business advisory firm Deloitte found in its report Entrepreneurship UK.

That compared with 3 percent of larger firms, that appear to be more aware and advanced in their preparations.

More than 70 percent of the SMEs said they thought London 2012 would have a neutral impact on sales.

The level of awareness of the impact of London 2012 among small businesses appears to be low, Rick Cudworth, head of the business continuity and resilience team at Deloitte, said in a statement.

One point larger companies will need to consider is how well-prepared the smaller businesses they rely on for supplies are for the Games as the indications at present suggest there is work to be done.

It is the first time Deloitte has looked at the preparations of SMEs, those generating revenues of 50 million pounds or less. It has previously concentrated on larger firms.

Transport was the main worry among those concerned SMEs, followed by staff availability.

An extra three million journeys are predicted on the busiest days of competition, while specially designated Olympic lanes, reserved to ferry tens of thousands of athletes, officials, sponsors and the media, will restrict deliveries.

We know from Sydney, Beijing and Vancouver that businesses tend to underestimate the sheer breadth and scale of the impact of the Olympic and Paralympic Games, and this survey suggests it could happen again in London -- despite the huge opportunity, said Tony Cohen, Deloitte's head of entrepreneurial business.

Companies large and small should be planning now to take advantage of increased demand and new customers.

(Reporting by Avril Ormsby)