As per title: 12 issues of the Economist for £1 (new subscribers only)
You can cancel at any time, so just make sure you do so after they take the £1 but before they take the next installment. Even if your forget, they'll refund you for any issues you haven't received when you do cancel.
They have the usual offer of 12 issues for £12 through their links, but I received this link in an e-mail from them yesterday. It isn't customer specific.
Offer ends 4 November so get in quick.