Apple has released a tool to create Mac OS X Lion portable recovery disks on flash drive or on external hard drives.
The Recovery Disk Assistant provides a way to reinstall Lion, run the Disk Utility or restore a system image from a Time Machine backup even if the regular backup partition is lost.
Lion installs a built-in recovery image on hard drive but users had raised concerns that if the hard drive was out of action then this would be of previous little help.
"This drive can be used in the event you cannot start your computer with the built-in Recovery HD, or you have replaced the hard drive with a new one that does not have Mac OS X installed," Apple said in the release notes.
A USB drive will need at least 1GB of free space and the tool can be downloaded from here.