There is an excellent book by Ann and John Tusa 'The Berlin Blockade' (1988. ISBN 0-340-41607-6
In the book the parlous state of food supplies in the British Zone of Occupation is discussed. The British administration was having to import food into our zone,from the UK ! the reason given is Russian intransigence and a strict adherence of the Potsdam agreement.
Whilst the American and French zones had problems,they could both cope with feeding the population, most of the Brit zone had been destroyed and, any agriculture was barely surviving. However,part of the PD forbad any 'trade between the occupied zones' so, supplies from one zone couldn't be seen to be going into another.
At the time, GB was supplying enough food to keep most of the German population,on or just above 1200 calories a day, official figures quoted in the book put most of the British population below 1200 per day,for at least 8 months after the end of the war...it also explains why basic food rationing went on for so long in the UK.