Starting a new set of accounts from an old one

[David Sumbler]

At the end of my 2010-11 accounting year I shall want to start a new set
of GNUcash files for the year 2011-12, using the same account hierarchy
as my 2010-11 accounts, and with opening balances equal to the closing
balances of the earlier accounts.

I am sure there must be an easy way to do this, but I can't find it.
Can somebody point me in the right direction, please?

David