Oh font of all knowledge, I seek some advice

I have had my car broken into this morning. The small triangle window, by the wing mirror, was smashed to gain access to my car. I have had some gardening tools nicked.

On ringing the insurance company they wanted to know my driving licence number. After frantic searching i cannot find my driving licence, as I haven't had to use it it in god knows how many years. Fair enough that they need this information.

I have been in my current address for eight years and can't actually remember renewing the licence. Therefore they want to know my old address which would be on my licence. They also want this along with my driving licence number which I keep in a book with passport number, various computer passwords etc. So no problems there.

However, they also want to know my National Insurance number too, which I am reluctant to give them. I hate giving out any details unless I absolutely have to.

Therefore should I definitely have to give them my National Insurance number, and for what reason do they need it?

Thanks, I know someone will be able to come up with the answer