Thanks Jeff,
I don't want a clone - i want to temporaily turn off replication (and therefore failover) and load a different db into the secondary which is now writable and run some tests. Then i will remove this db and run a basebackup to reinstate a copy of the master and turn on replication again.
So :
shutdown secondary
change hba_conf so primary cannot connect
rename recovery.conf
start db
load new db
run tests
shutdown db
basebackup db from master
revert streaming settings
startdb
thanks.