Cameron could reach a deal at an EU summit in February, paving the way for a public vote as soon as June.

Following are the views of business leaders:

AEROSPACE AND AIRLINES

Ryanair Chief Executive Michael O'Leary:

"We're very actively supporting the campaign to keep the UK in the European Union. There's absolutely no doubt that the UK economy is better off in Europe than outside of Europe."

Rolls-Royce (>> Rolls-Royce Holding PLC) President of Aerospace Tony Wood:

"Uncertainty is unhelpful in any businessman's mind. This is a very long-term business. It takes us 10 years to design an engine, we make it for 15 to 20 and we continue to service it for another 15 to 20. Any kind of uncertainty politically is not good."

Aircraft parts maker Meggitt (>> Meggitt plc) CFO Doug Webb:

"We want the business environment to be as supportive as possible and being able to easily trade across borders is important. Equally, being able to trade in an efficient way with as little red tape as possible is important. I guess what we would like to see is the best balance across that."

AUTOMOTIVE

Ian Robertson, BMW (>> Bayerische Motoren Werke AG) Director for Sales and Marketing:

"The UK has the most diverse car industry in Europe and is the fourth largest market of BMW Group worldwide. From an industry perspective we would therefore regret seeing the UK leave the EU."

Chief Executive of carmaker Opel (>> General Motors Company), which owns the Vauxhall brand, Karl-Thomas Neumann:

"We have plants in Luton and Ellesmere port. We will not turn our back on England. If Britons voted to leave the EU, life would carry on. We would continue to find ways to invest."

CEO of Volkswagen-owned (>> Volkswagen AG) British brand Bentley Wolfgang Duerheimer:

"Volkswagen Group has 110 locations around the world where they produce cars. That means they are not in any case reliant on the UK so if the situation changes dramatically, future decisions need to be considered among the circumstances you face."

BANKING AND FINANCE

Colm Kelleher, President of Morgan Stanley (>> Morgan Stanley):

"If Britain were to leave Europe you would see a significant backlash against London as a financial centre."

Citi's (>> Citigroup Inc) UK head James Bardrick on what could happen post-Brexit:

"We would have to operationally change the business and reallocate certain businesses back into the EU. That's not technically impossible ... but enormously costly and enormously inefficient ... and will mean the scale of our activities here will reduce."

British Bankers Association Chief Executive Anthony Browne:

"Some banks have recently moved operations and jobs out of the UK due to punitive hikes in bank taxes. Other banks have deferred decisions about whether to invest in Britain until after the referendum."

Standard Life Investments Chief Executive Keith Skeoch:

"This would be a shock that would register about 15 on the Richter scale," he said, referring to the possibility that Britons might vote to leave the EU. You want to make sure the rights you have today will persist for the next 20-30 years."

(NB - the highest Richter scale earthquake ever recorded was 9.5)

ENERGY, OIL AND GAS

Chief Executive of oil giant Royal Dutch Shell Ben van Beurden was quoted as saying by The Sunday Times newspaper:

"We are a company with a strong heritage in the UK and on the Continent. There would be a real break between the two, which would affect freedom of movement of staff, trade — we would be impacted.

"There will be a path of divergence, and that will have all sorts of inefficiencies. That’s not good for companies like ours that thrive by there being no barriers. That is a fundamental economic aspect of it."

Chief Executive of BP (>> BP plc) Bob Dudley told the BBC:

"Being outside the EU would be worse for the country as many of the rules would still apply and Britain would be in danger of losing influence on the world stage.

"There are lots of technical tax reasons, trade flows, regulation, that would make it better for our business and the energy business in general, the oil and gas business, (if Britain) were a part of Europe."

National Grid  (>> National Grid plc) Chief Executive Steve Holliday:

"We cannot afford to lose the access to (European) energy supplies and interconnection, whatever the framework is eventually. Being part of the European energy market is unquestionably essential for the UK."

HOUSEBUILDERS AND ESTATE AGENTS

Managing Director of London-focused housebuilder Berkeley (>> Berkeley Group Holdings PLC) on what could happen if Britain leaves:

"My concern would be around inward investment into London and it would slow down the growth of jobs and its influence."

"If it retained less influence and less jobs, it will grow less quickly so it would actually need less homes built."

Head of Commercial Research at real estate group Savills (>> Savills plc) Mat Oakley:

"The biggest risk to the commercial markets is that pre-vote period. Is it going to be three months, six months, nine months of speculation and the market may just go slightly quieter.

"We have spoken to a number of people who've said we'll seriously consider moving our headquarters functions ... and our growth over the medium term to long term may well be more skewed to the EU ... if the UK were to leave."

INDUSTRIALS AND CHEMICALS MANUFACTURERS

Chief Executive of industrial equipment hire group Ashtead (>> Ashtead Group plc) Geoff Drabble:

"We have an ageing population in a small nation that needs to have skills in order to be globally competitive. And in a market that is becoming ever more global, I really struggle to see how increased isolation improves that situation."

JCB Chief Executive Graeme MacDonald:

"I really don’t think it would make a blind bit of difference to trade with Europe. There has been far too much scaremongering about things like jobs. I don’t think it’s in anyone’s interest to stop trade. I don’t think we or Brussels will put up trade barriers.

"What is needed is a lot less red tape and bureaucracy. Some of it is costly for us and quite frankly ridiculous. Whether that means renegotiating or exiting, I don’t think it can carry on as it is. It’s a burden on our business and it’s easier selling to North America than to Europe sometimes."

INSURANCE

Chief executive of the Association of British Insurers Paul Evans:

"In the UK, the real political uncertainty for our sector comes from the dual and interconnected possibility that the UK could leave the EU and that the UK could dissolve if Scotland voted to become independent. Even five years ago, the likelihood of both would have seemed far more remote than they do now and so we certainly cannot be complacent."

RECRUITMENT

Steve Ingham, chief executive of one of Europe's largest recruitment firms Michael Page (>> Michael Page International plc), told Reuters:

"I am concerned about the disruption, because it causes uncertainty and uncertainty means that people are unprepared to make decisions. It's not good for a candidate thinking about moving job, and it's not good for a client and that's more a concern."

RETAIL

Chief executive of fashion retailer Next (>> NEXT plc) Simon Wolfson:

"My view is that if we have Brexit then what will make a difference isn’t so much the fact of coming out of Europe but whether the policies pursued by the government post Brexit are ... free trade, open, positive, embracing a global trade view or a protectionist one. I haven’t made my mind up yet. I’m going to wait and see what deal the Prime Minister is able to secure. That matters."

Marks & Spencer  (>> Marks and Spencer Group Plc) Chief Executive Marc Bolland:

"I feel that some of those (European) reforms can be done and should be done. Actually, I think the best judgement call for Britain to take is to see what the result of the reforms are before they take a point of view (on EU membership)."

"Europe is very important for Marks & Spencer because we have over 100 stores within the EU."

TELECOMS

Vodafone (>> Vodafone Group plc) Chief Executive Vittorio Colao in a letter to Italian newspaper La Repubblica:

"I think (Cameron) is right to say these reforms would be good for the entire EU and not just the UK, showing clearly the advantages all Europeans would get from them.

"European companies have been asking for these reforms for years, sadly with limited results, while our competitors in the United States and Asia continue to grow more quickly."

(Reporting By UK bureau and EMEA corporate finance team; compiled by Costas Pitas)