Hello everybody.
Thank-you so much for your comments. I really do appreciate your help. After liasion with the very helpful Adrian, at Kingsley Cars Oxford, we have figured out that the second nipple or spiggot is used on only a limited number of classics. This is what he sent me:
"There should only be the one nipple which goes to the fuel pressure regulator.
BUT on some models a vacuum pipe, from a second spigot, operated a hot water valve via an electrically switched valve.
The hot water valve is located on top of the right hand rocker cover in a Y connector in the water pipes. The electric valve is located on the bulkhead just behind it.
http://lrcat.com/#39/4/49254
The tail of pipe number 8, I think, should go on the 2nd nipple."
Indeed my classic does have this hot water valve so I have ran a pipe from the 2nd spiggot to this valve. I will try it at the weekend and report back.
Those guys at Kingsley Cars are very knowledgeable and for someone to e-mail at 21:30 says alot for the commitment they have.
Thanks again
David.