If you're buying from a sole trader, or perhaps engaging the services of a consultant who operates their own business, there should be no problem with the arrangement. (He/she would be obliged to include the value of the alcohol as part of his/her income when submitting his/her tax returns but that's nothing to do with you).
However if the recipient of the alcohol is an employee of a firm, then there could possibly be implications of bribery if you were providing him/her with benefits that weren't going to his firm, especially if it appeared that you were seeking to get him to offer you a better deal with his company.
The scale of things would also be important though. My father used to receive an annual bottle of Scotch at Christmas from a guy that he negotiated contracts with on behalf of my father's employer. A single bottle of Scotch once a year, when contracts worth hundreds of thousands of pounds were passing between the two firms, could hardly have been seen as a bribe. However if you're thinking of sending someone (who isn't a sole trader or consultant) several cases of Dom Pérignon in order that he'll get his firm to offer you a lower price for a contract, then bribery definitely comes into it!