Normal market size - currently 5,000 although up until recently it was 10,000. The more the share is traded, the higher in general this figure will go. It is set by the exchange, but with pushing and pulling by the MMs who would like it to be as low as possible.
Edit. Not that it makes much difference. We have just seen 100k go through an hour late @ 94.5p. Can anyone really believe that the MM hasn’t managed to cover this amount with another trade, or else why would the sp remain unchanged? In the end, the sp is the sp.