Anyone with the remit of generating publicity for a product or service will recognise the huge benefits of setting up a Twitter account. After all, it's hard to turn down a free marketing tool that opens up new audiences, great information gathering opportunities and drives people to events, websites, helplines etc. Twitter is certainly an effective way of building brand awareness and sales. However, as can be seen from this article in the Daily Mail online, http://www.dailymail.co.uk/news/article-1345382/Stop-Tweeting--court-Watchdogs-crackdown-celebrities-plug-products-Twitter.html, those not declaring they have a financial interest when tweeting about a product could soon find themselves in rather hot water.
Those connected with the Chartered Institute of Public Relations, www.cipr.co.uk, will know that they (like other industry bodies) have long had a policy in place that outlines the necessity of full transparency at all times and it's well worth a look if you're not au fait with best practice. My suggestion would be to do it soon or live with the consequences.