Can anyone persuade me (aged 30, married, no kids) as to why I would need a will and couldn't just rely on The Law?
You may be surprised to learn that a spouse does not automatically inherit everything from the other (
The Probate Service - Why make a will? ) Now that may not bother you, or you may not think it affects you, that's fine. Often conditions change without you noticing (things like the value of your property increasing) so that can affect your thinking.
Ultimately it is one of those things that is Very Good to have and it is also Very Good to do it when you don't have a need to. My wife and I ended up writing ours after she had been diagnosed with cancer, and it felt horrible. Do it precisely because you don't have to.