Working with DueDil, a source of free private-company information in the UK and Ireland, Investec has analysed data from 24,000 companies with an annual turnover of between £10m and £200m, employing over six million people and accounting for nearly £1,000 billon of turnover each year. The index looks at four indicators:

· Annual Turnover
· Operating profit
· Return on capital employed
· Employment levels.

The data for the Investec MMI has been analysed back to January 2006. In that time the index has gone from 100 to 135.4, which is comparable with the performance of the FTSE 250 index, usually taken to show the performance of mid-market stocks, with the index currently growing at 4% per annum. Annual growth in operating profits for the 24,000 businesses is running at just over 8%, higher than the rise in "money" GDP of 5.4%. Return on capital is a healthy 7.4%.

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Ed Cottrell, head of growth & acquisition finance at Investec, said: "The UK's mid-market companies account for nearly £1 trillion of revenue and a quarter of all private sector jobs, yet their contribution to our economy is either overlooked or misunderstood. The data used to create the Investec Mid-Market index shows that the owners of these businesses invest for the long term, are not distracted by quarterly results and share price fluctuations, and are reliable employers and therefore provide the foundation of our economy."

Philip Shaw, chief economist at Investec, said: "While there is a great deal of information and analysis of Britain's major companies, there is relatively little known about the mid-market. Given its importance to the economy, this is a major omission. We aim to put this right with the Investec Mid-Market Index and show the outstanding contribution of the British Mittelstand."

The Investec MMI will be published twice a year as part of a new programme that will showcase the strength and importance of Britain's mid-market, says Investec. This will include a listing of the 100 fastest-growing private companies in the UK, published every six months, and an annual Mid-Market Summit to highlight their achievements.

Investec Structured Products, part of Investec, is a corporate member of the IFP.