It's a risky time to be owed money. Contractors and clients in the property world are falling like flies.

So it was quite disturbing to calculate that £9 billion is outstanding in trade debt to the UK's building specialist contractors. And that doesn't include all the specialists involved in civils and groundworks associated with building work.

The figures comes from some analysis I am doing on payment issues for the forthcoming CJ Top 100. I thought I would look into trade debt and trade credit and also have a particular look at building specialist firms.

Here are the figures from a survey of financial data from more than 6,500 firms SIC coded 45 of which almost 3,000 companies are building specialists. The data have been kindly provided by Corpfin, part of Experian.

On average construction firms manage to stay strongly cash positive on trade debt and trade credit. This is not true however of specialist firms.

The specialist firms in the sample came out at about 3.8% of turnover down on the deal, having to stump up more cash to suppliers than they get from their clients. This compares with around a 2% positive cash balance for the full sample of firms.

According to Government data the building specialists (SIC code 453 and 454) turnover about £65 billion, which suggests on the basis of the above numbers that they have to find about £2.5 billion to fund the gap between trade debt and credit. Some of this will be found from their parent companies, which in some cases will be net positive on the deal.

The numbers also show that what is owed to building specialists by trade debtors amounts to about 14% of turnover. That equates to more than 7 weeks of trading. And, assuming the sample is fairly representative, that means they are owed £9 billion.

There is some good news in that the figures don't appear to be getting worse, looking back at previous years. Although they may be as there may be, of course, an element of survivor bias in the numbers, with the more over-extended firms falling by the wayside and the more prudent surviving.

Either way, with clients falling fast, £9 billion is a lot of money to have at risk.