Basic loss per share is calculated by dividing the loss attributable to equity holders of the Company by the weighted average number of ordinary shares in issue during the period, excluding ordinary shares held pursuant to the Group's JSOS which are accounted for as treasury shares.

Diluted loss per share is calculated by adjusting the weighted average number of ordinary shares outstanding to assume conversion of all dilutive potential shares. The Company has two categories of potentially dilutive shares, namely share options and shares held pursuant to the JSOS.

There was no difference in the weighted average number of shares used for the calculation of basic and diluted loss per share as the effect of all potentially dilutive shares outstanding was anti-dilutive.

Basic and diluted loss per share has been calculated as follows:

53 weeks
ended
2 December
2012
million
52 weeks
ended
27 November
2011
million
Issued shares at the beginning of the period 522.1 521.0
Effect of share options exercised in the period 0.3 0.6
Effect of treasury shares disposed of in the period 0.1
Effect of shares issued in the period 0.9
Weighted average number of shares at the end of the period 523.3 521.7
£m £m
Loss for the period (2.4) (0.5)
pence pence
Basic and diluted loss per share (0.46) (0.10)

The only transactions involving ordinary shares or potential ordinary shares between the reporting date and the date of these financial statements were the exercise of 29,805 share options.