I used to write wills for a living. Here's what I advise:
1. Forget about using any 'kits'. They can easily fail to ask you important questions (e.g. if you leave money to X, what should happen if X dies before you do?).
2. Get hold of a copy of this book:
Amazon.co.uk User Recommendation
(It's in almost every library in the country. It won't matter if you find a slightly older edition; the basic rules won't have changed).
3. Draft your own wills, based upon what you've read in the book. (Simply type them onto plain paper).
4. If you're 100% confident that what you've produced fully reflects your wishes and is completely watertight, sign your wills in front of two witnesses and get them to add their signatures. (It's all explained in the book).
5. If you've got any doubts about what you've produced, take your drafts to a solicitor and get him/her to 'tidy them up'
6. When you've made your wills, tell the executors (and/or beneficiaries) that you've done so and where you've put them. (It's likely that thousands of wills get ignored every year, with the intestacy rules being applied instead, simply because the wills are never found).