Soph
You should speak to an Independent Financial Advisor (IFA) who will assess your needs and make recommendations.
See thread http://www.moneysupermarket.com/community/forums/t/advice-needed-for-first-time-life-asurance-buyer-18878.aspx?Source=MSSEMS , this provides some issues to think about before you speak to IFA.
Once you know exactly what you need shop around. See moneysupermarket Life Insurance page which contains a guide.http://www.moneysupermarket.com/LifeInsurance/uk-life-insurance.aspx
Personally I would contact my bank first of all, if you have a good relationship with them. They are not always the cheapest but I have personally found that they do provide a good service.
Huckster