In message .com,
writes
At last we've finally paid off our mortgage and have been sent a huge
bundle of deeds and papers relating to the house.

My first thought was to get a fireproof document storage box to keep
them in, but some of the papers are too long ( 360mm ) to fit in any of
the boxes that I've seen and it isn't very practical to fold up the
bundles of paper to fit them in a smaller box.

Mine are in the filing cabinet along with all the other important
documents

What real importance are they ?

You could always scan the important parts (e.g. boundaries) and store
them on-line somewhere

--
geoff