"The Society was doing its best to see that the supply of beer to canteens, and particularly to the Forces through NAAFI and otherwise, was at a satisfactory level. In many cases breweries asked to supply canteens and messes had replied that they had no surplus beer available, with the result not only that beer had to be brought from considerable distances but also that the distant brewers supplying were only able to do so by reducing the supplies to their own customers. It had to be realised that the supply of canteens with reasonable quantities of beer was most desirable and the Committee recommended that brewers should be urged to consider carefully applications made to them for such supplies and to see whether a limited quantity could not be made available even if it involved some reduction in the supply of beer available for their own houses."
The Brewing Trade Review, October 1943, page 301.
Most brewers were struggling to supply their own tied houses. It wasn't surprising that there was an increased demand for beer. Large numbers of young men from all over the world had been brought into the UK. Many for the planned invasion of France the following year.
Recognising this, the government had allocated extra raw materials specifically to brew beer for the forces.
"Beer for the Forces
There is an aspect of the activities of the Brewers’ Society which is seldom referred to in these columns, but it is one which engages the Society’s constant attention and is a material contribution to the war effort. This is the arrangement of supplies of beer for the large number of canteens and messes established throughout the country for our own troops and those from overseas. Last year the Society set up a special Committee to deal with this matter, and among other things it was necessary for the Society to depart from its usual course so far as to act as a merchant for the distribution of materials specially made available for this purpose. The Committee has been gratified at the ready response met with from brewers, large and small, the majority of those approached having been ready to cooperate wholeheartedly in seeing that the soldiers, sailors and airmen quartered in this country and proceeding overseas do not go short of a reasonable supply of beer. Nevertheless, there has been difficulty in many districts in finding sufficient supplies. The exigencies of war put down large numbers of men in areas where in normal times there is not a very large demand for beer and which are therefore not sufficiently equipped with breweries close at hand. In such cases it becomes necessary to send beer into the district from breweries further afield.
It should be said that this provision of beer for canteens and so forth is not done without a good deal of sacrifice on the part of breweries of the reasonable demands of their regular customers and of the calls upon them by their own licensees. It is a sacrifice which we believe most brewers are ready to make in the National interest, but it is one which cannot in the nature of things be evenly spread because the demand for beer for this purpose is subject to a good deal of variation as between district and district. But the Society endeavours to be as fair as possible in calling upon the various breweries to assist the forces as occasion arise, and it is hoped that it may continue to rely upon receiving the willing help of every brewery concerned."
The Brewing Trade Review, October 1943, page 307.
The forces gathering in the UK weren't spread evenly across the country. There were proportinally far more in the South of England, were D-Day forces were being assembled and in the East of England, where most of bomber command was based.