BARCELONA (REUTERS) - Almost three quarters of Spanish business leaders fear Catalonia's plans for an independence referendum on Oct 1 could harm the country's economy, according to a study by Deloitte published in Spanish newspaper El Pais.

Madrid has condemned as illegal plans by the northeast region's government to hold a referendum on seceding from Spain and, if the yes vote wins, declare independence unilaterally within 48 hours.

Last week, the Spanish government said Catalonia would lose access to some public funds if it used the money to prepare for the unsanctioned plebiscite.

Nationwide 74 per cent of 265 business leaders surveyed believe the Catalan independence movement threatens the Spanish economy, while 43 per cent of those based in Catalonia itself agree, according to the Deloitte Survey of Companies study commissioned for El Pais.

Despite concerns about the political deadlock over Catalonia, confidence in Spain's continued economic growth remains high, according to the poll.

Eight out of 10 directors polled said the economy had improved in the first half of the year. Seven out of 10 expect to bill more in the second half of the year than in the first six months.

Spain has surpassed expectations for GDP growth this year. Last week the International Monetary Fund said it expected Spain's economy to grow by around 2.5 per cent in 2018, up from its previous forecast of 2.1 per cent.

Opposition to seceding from Spain rose slightly to 49.4 per cent in June, according to a poll by the regional government's Centre of Opinion Studies, from 48.5 per cent in March.