I eventually took the plunge and removed the Christmas tree adaptor. I had to hacksaw one of the branches off to get it to clear the handle as its a one piece casting, but it came out without any problems after that. The fitting in the pump takes a 3/8 BSP fittings so I was able to get a 1/4 turn valve to fit in its place and a normal BSP-8mm hose barb.
Just a watch out if anyone else goes down this route, there is very little clearance between the port and the pump handle. I had to take the knob off the valve to get enough room for it to screw in and then refit it afterwards.