From the 11th to the 13th, you can exchange up to two non energy saving light bulbs for Energy saving ones. Two per customer.
The blurb from the press release:
Mayor of London launches energy efficiency light-bulb giveaway to help tackle climate change
The Mayor of London Ken Livingstone today (Tuesday 8 January) launched London's first 'light bulb amnesty' - offering Londoners free, energy efficient light bulbs in exchange for old-style, energy guzzling bulbs to help cut climate change emissions and energy bills.
London's first light bulb amnesty will take place from Friday 11 January to Sunday 13 January, in conjunction with B&Q and British Gas. Londoners can take a traditional light bulb from their home to any of the 28 London B&Q stores and, in return, receive a free, energy efficient light bulb, provided by British Gas. A new poll undertaken by Ipsos MORI on behalf of the Mayor indicates strong interest in a light bulb amnesty with nearly two thirds of respondents saying they are likely to take part in the scheme. *
Each energy efficient light bulb can save households £7 a year and up