THE chief of DIY giant B&Q has entered the independence debate with a clear message to Scots: don't do it yourselves.

Sir Ian Cheshire, the chief executive of Kingfisher which owns the home-improvement chain, said the company was concerned about questions surrounding Scotland's future.

He said uncertainty over the currency was a particular concern, as B&Q faced the costly task of repricing 45,000 product lines if an independent Scotland was unable to share the UK pound.

The head of the UK's biggest defence firm, BAE Systems, has, meanwhile, warned employees a vote for independence could risk jobs and pensions while the chief executive of Diageo, the world's biggest producer of Scotch whisky, said a decision was for "the people of Scotland" to make but remaining part of the European Union was "extremely important" for the company and industry.

The business leaders' interventions came on the first day of the referendum campaign proper, when legally binding rules came into force.

Leader campaign organisations Better Together and Yes Scotland marked the day with separate events in Glasgow.

Better Together's campaign director Blair McDougall joined activists in the city's Govanhill area while actor and independence supporter David Hayman visited Yes Scotland's HQ.

Also on the first day of the so-called regulated period covering the 16 weeks before polling, Business for Scotland, a pro- independence group linked to Yes Scotland, launched a campaign to contact 250,000 business people.

Sir Ian, who also runs the Screwfix hardware chain, spoke out during a visit to the UK's newest B&Q store in Port Glasgow. He made it clear the company would continue trading north of the Border whatever the outcome of September's referendum.

He said: "Of course independence is possible; the question is, is it better than what we've got? How do we think this situation looks from a purely business point of view? Where we have got to is the conclusion that we think staying in the Union, being part of the UK, is the better answer."

In a warning on the impact of a possible new currency, he said: "We would need a separate pricing structure which would create a lot of cost and complexity."

Ian King, the chief executive of BAE Systems which owns the Govan and Scotstoun shipyards on the Clyde, told staff in an internal blog that while the referendum was a "political and personal decision for the people of Scotland", a Yes vote could lead to an unpredictable future for the company and its 3500 workers north of the Border.

He wrote: "As far as our business is concerned, at present, we have certainty and stability in relation to those elements of our business which are located in Scotland, especially in Glasgow.

"This is based on an expectation that the Government will make their major production ­decision for the next generation Type 26 Frigate by the end of this year. Scotland became independent, we would no longer have that certainty and stability.

"We would then have to talk to our major UK customer, the MoD, and jointly work out a plan for the future."

Speaking about the Kingfisher chief executive's comments, Tony Banks, chairman of Balhousie Care Group and pro-independence group Business for Scotland, said: "We welcome Sir Ian's confirmation that his companies and associated jobs will remain in Scotland after a Yes vote.

"We will seek a discussion with Sir Ian to clarify some misconceptions about independence promoted by the self-styled Project Fear. There will be no barriers to trade and, in fact, significant opportunities through the tax system to reduce costs for companies operating in Scotland."