The absence of pre-lettings is largely responsible for the downturn, with pre-let construction activity down 33% on the previous six months. Carl Potter, National Head of Business Parks at GVA Grimley, said: 'Over the course of GVA Grimley's last three business park reviews, we have witnessed a decline in speculative development and a slow but steady increase in availability. The last six months, though, have seen a dramatic and sudden increase in vacancy rates - a trend attributed to both the continued downturn in the technology sector and the aftermath of September 11.'

Availability of space on UK business parks has been increasing steadily since a trough of 5.2% in December 1998. And the amount of vacant space rose sharply between June and December 2002 from 6.6% to 8.3% of stock. In total 4.8 million sf of business park space is now standing empty.

But Potter said the market fundamentals remained solid. 'Although at first glance the figures might seem discouraging, they do indicate that things aren't all bad,' he said, 'Although there has been a drop in the number of lettings, this is still above average since 1996. Furthermore, developers are still active - particularly in the speculative market - reflecting an underlying belief in the business parks market.'