OK, if you are sure that the incoming water is at mains pressure, then there is no need to have a separate supply to the washing machine and your hose...I suggest that either the stop cock isn't turned fully on, or there is an isolator valve somewhere in the pipework that is restricting the supply. The only other thing I can think of is if you have used one of those self cutting outdoor tap kits for your hosepipe connection, then consider a proper 'tee'd off connection. Try disconnecting your washing machine from its tap, and trying the water flow from there. It should be just the same at the hose outlet.
John
May 2009