The Nokia 100 has been spotted in Tesco (Pontarddulais, specifically) for £1, limited to 2 per customer.
Ideal as a backup or emergency phone to chuck in your glove box, Nokia 100 specs include a 1.8in display above a full numeric keypad. Built-in FM radio and flashlight, too.
In-store only. Not available online.
Nokia 100, £1 in-store @ Tesco
(Thanks to stellaframe5 at HUKD)