Why import members who don't have a valid email address?

If they are in a group with someone who has a valid email address, that person can login and renew for all members in the group (e.g. parents renewing their children's subscriptions).  Any email sent by the system to someone without a valid email address is automatically sent to the group admin with a valid email address.

For those who are not in a group, or no one in the group has a valid email address, they can still login (using their @temp.webcollect.org.uk email address).  You would however need to send them a letter with their login details.  The simplest way to do that, is to use the Subscription Renewal letter (if you import the subscriptions).  Or use the prepared letter, and include the [sign_in_details] tag.