Trust Funds - locating a lost trust fund

Hi,
My grandfather set up a trust fund for my father probably about 60 years ago when he divorced my grandmother, it could hold a fairly substantial sum, the problem is that my grandfather never passed the details to my father. My grandmother died a long time ago, and my grandfather is very old, senile, and does not talk to our branch of the family because of the nasty divorce.

My father still enjoys approx £300 per month from this trust fund but it is paid directly from my grandfather's bank account (probably because he is the guardian of the trust), so we can't do a trace at the bank to find out where the trust is held. There is also the possibility that when my grandfather dies the trust fund will be lost forever because nobody knows about it.

So my questions are:
1. Does anyone know how to locate a trust fund?
2. How do you get hold of the trust document which outlines the trust details?
3. What would the value of the whole trust be if £300 income per month is generated?

Many thanks
Britgirl