The behaviour of the FTSE 30 share index is examined over a period fro
m November 1988 to May 1994. We examine whether the index exhibits dif
ferent time series behaviour during the time that Sterling belonged to
the ERM to that observed in the pre- and post-ERM period. We show tha
t the random walk behaviour, which would be expected under the Efficie
nt Markets Hypothesis (EMH), occurs during the period when Sterling be
longed to the ERM but for pre-and post-ERM membership period the index
does not appear to follow a random walk.