Ocado

There are many posts on TFL that recommend trying to source fresh yeast from your local, large supermarket bakery department - when it is a bakery not a tanning salon for partially baked loaves.  Also, Richard Bertinet will supply good fresh yeast but either in 500g blocks or on a regular "plan".  There are also some specialist suppliers such as NiceisLife (Italian produce http://www.nifeislife.com/ ) who also sell small packs of fresh yeast.