Dog in the Manger

I have been asked by one of my overseas readers to explain the expression Dog in the Manger  which I used in my post  yesterday.
A dog lying in a manger, or hay feeder for cattle, cannot eat the hay but prevents the cattle eating it.  It is being selfish by preventing others from using something it cannot use itself.  In the example yesterday  BW did not want to use the mooring itself and has, indeed opened up the yard as a public car park during the water crisis.  However the enforcement officer did not want us to moor there. BW, as personified in the enforcement officer, was acting like a dog in  a manger.