When developing your subscription process, legal considerations are extremely important. Legislation (created with SPAM prevention in mind) will have a major impact on how or if consent is required; what information you collect; how you handle your data and even unsubscription.
In the UK, there are three pieces of legislation that you need to comply with – however, it is important to bear in mind that legal compliance is only the first step. Subscriber perceptions of your email marketing activity are just as important. The fact that your campaign is legal will not stop subscribers from hitting the spam button and damaging your reputation with an ISP.