Last year small businesses' credit turnover, or income, grew at its strongest rate since 2000, research by Barclays found.The value of payments into the current accounts of the lender's small business customers was up 20% from 2000, according to the bank's Small Business Income Index."This reflects the strength of cash-flow to the business population and the resources available to them. It is also closely correlated with official measures of economic activity," the lender said.Having already recovered in 2013 to its pre-recession peak levels, 2014 saw a step change in the strength of business activity with income rising by nearly 8%, the fastest rate in 14 years.Real estate and construction businesses saw the biggest income growth in 2014, accounting for more than one-third of small business income growth of the year, while the accommodation, education and health sectors also saw a positive growth from 2013.London was the region with the highest overall customer income growth, followed by the South and North West.The index tracks 600,000 small business customers with an annual turnover of less than £5m each.