Figures suggest that more than 4 million people are now relying on the scheme – an eighth of the workforce. It covers 80pc of employees’ wages up to £2,500 a month.
But there are questions over double and even triple-counting of people who have been furloughed for several part-time jobs.
Tej Parikh, chief economist at the Institute of Directors, called for more clarity.
He said: “We’d encourage Government to err on the side of more transparency when it comes to publishing statistics.
“The Government has rightly won credit for being agile in adapting its economic policies, and open discussions based on real-time feedback can help this process.
“While double-counting may be affecting the overall number of individuals affected, it’s still valuable to be able to put a figure on how many jobs are being protected by the scheme. Gauging which sectors are engaging most with the system can help our understanding of the current impact on the economy.”
The scheme has proved popular with companies as incomes have dried up, endangering the employment of millions – but lobby groups have called for more flexibility and some problems still remain.
As many as 600,000 furloughed staff are being asked to carry on in their jobs in a breach of the rules, according to a survey from economists at the University of Oxford.
They found that 15pc of those furloughed have been asked to do more work even as the Government pays their wages, indicating the scheme is being abused on a significant scale.
HMRC urges those who are faced with these demands to report their employers for fraud.