Britain's entrepreneurs now spend more of their spare time worrying about their business despite putting in longer hours, a new survey says.

Small business owners now spend an average of 55.4 hours a week at work, with over a quarter working more than 61 hours and a further 15 per cent clocking up more than 70 hours, according to the RBS Living Business Survey.

Those working in agriculture and mining put in an average of 64.9 hours, hotly followed by those in the hotel and catering industry. But people working in the retail sector actually saw a drop in working hours from 54.3 in 2002 to 53.4 in 2005.

Businesses in Yorkshire and Humberside saw their hours increase significantly from 50.9 in 2002 to 60.3 in 2005.

But despite working longer hours, entrepreneurs are also spending more of their free time thinking about their business - with those leading a bigger team of employees worrying more.

Those with five to ten employees spend an average of 17.6 hours a week mulling over work issues whilst those with more than 11 staff clock up an extra 20.2 hours.

Over a quarter of small business owners say they are stressed by late payment of invoices, whilst 17 per cent claimed customer related issues gave them a headache. Entrepreneurs with a larger team of employees were more likely to be stressed by staff problems but few cited problems with suppliers, the bank or competition from other businesses.

But 38 per cent said they liked being their own boss, especially those working in the construction and wholesale sectors as well as those who are based in the East Midlands and Yorkshire and Humberside. Around 12 per cent were motivated by self-fulfillment and a further 10 per cent by wanting to make money.