To invite people to join a group on sustainable hackney first go to the page for that project. At the bottom of the page click on the link + Invite More.
You can then:-
Import from Web Address Book: Just type in the address and the password for an email account on AOL Mail, Gmail, Yahoo! Mail or Hotmail — you'll immediately be able to invite any of your contacts to join.
Enter Email Addresses: If you have a particular set of email addresses that you want to send invitations to, you can enter or paste these email addresses in this section. Enter multiple email addresses into the "Send To" field, separated by commas.
You can also use the invite link on the invite page. Copy this into an email and send it to the people you want to invite.