A Long Shot - Locating Savings from deceased relative

Hi,

This is going to be quite a long shot, and will need a lot of explanation to fully explain, so apologies if it is confusing or a bit muddled. Will do my best to be clear.

When I was younger, my dad passed me a letter that was from my grandfather, relating to an account with funds in for me to withdraw when I reached 18. Unfortunately, it was only to be given to me when my grandfather passed, so essentially worked I guess as some sort of child savings bond? The idea, apparently, was to give each grandchild £100 that wouldn't gain interest to make sure we all got the same, given age differences.

Anyway, years went by, the letter sat in my room in what I thought was a safe place, waiting for when I turned 18 so I could claim it. Alas, 18th birthday arrives, and I'd forgotten about the letter for quite some time, but one day remembered I had it. Could I find the letter? Not a chance. Still, to this day, I have no idea where i put it.

The big problem I have here is that I don't know what company it was with, what account it was in or what details it was stored in. I know the address I lived at at the time I got the letter, and I can get information regarding my grandfathers name I'm sure so that it can be found, but I have no idea where to start. I've filled out a Lost My Account form but don't even know if I've done that right to be honest. Anyone have any suggestions at all? I've asked my parents and they can't recall the company or account either.

Many thanks in advance.