Embed survey links in campaigns email templates but need a contact ID
I need to embed a custom survey link in my outgoing email marketing campaigns footers.all footers.
These have several custom variables to identify the user, and I'm using merge tags there which is fine for them but in order to pull these responses back to the crm record I need a merge tag for the contact_ID and this is not an option in campaigns.
Please advise on how I could achiecve this?