UK competition officials have launched a probe into Diageo's purchase of what is in effect a controlling stake in Whyte & Mackay owner United Spirits by issuing an "invitation to comment".

The Office of Fair Trading said it would investigate whether the deal signed between the Johnnie Walker owner and Indian tycoon Vijay Mallya would have a detrimental impact on the spirits market.

The focus is likely to be on United Spirits' Whyte & Mackay business, owner of brands including Jura and Dalmore. Diageo, behind the likes of Buchanan's and Lagavulin, is the world's biggest Scotch whisky producer.

The OFT will consider whether the combined company will have an excessively dominant position in the UK market.

A key issue in the competition decision will be whether 
Whyte & Mackay's own-label whisky production is viewed as being in the same category as Diageo's low-end Bell's whisky brand.

At the beginning of this month Diageo has spent £344 million to acquire another 14.98% stake in Vijay Mallya's United Spirits business.

This took its stake to 25% after it earlier acquired a 10% stake in the Indian drinks giant through the issuing of new shares. With a voting agreement, Diageo has control of the business.

It had intended to take a majority stake but this was stymied by a surge in United Spirits' share price above Diageo's open offer bid.

The Office of Fair Trading said any representations should be made by August 2.

The OFT has 40 working days to come to a conclusion. It can opt to clear the merger or it could ask the companies to agree to sell offer certain brands or businesses.

If it regards neither of these options as being possible then it can opt to refer the merger to the Competition Commission for a more thorough investigation.