Storage group Big Yellow swung into the black for the full-year and said it has seen an improving level of demand since spring last year.The group made a profit before tax for the year ended 31 March of £10.2m compared to a loss of £71.5m last year, thanks to the increase in the valuation of its open stores coupled with the improved recurring profit offset by the write down of assets in the course of development. Revenue for the year was £58m, a reduction of £0.5m, principally caused by a reduction in short term tenant income of £0.4m. The value of the open store investment property portfolio at 31 March 2010 was £761.6m, up from £735.1m at 31 March 2009.The group said it has seen the start of the usual seasonal pick up in the quarter ended March, which was stronger than in 2009. Storage revenue for the fourth quarter increased to £13.7m from £13m for the same quarter last year.Chairman Nicholas Vetch said: "There is clearly a recovery under way in the performance of this business evidenced by year on year quarterly growth and the levels of reservations, phone calls and web enquiries coming into the business.""The pace of this recovery will to some extent depend on continuing improvement in housing transactions and economic growth, which drives business and consumer confidence."