Your text...
"I have 2 x 1 gang 2 way L/switch in the hall upstairs and a 2 gang 2 way down stairs. All are driving the upstais hall light."
Does this mean?
You have two separate (single gang) switches in different places upstairs - downstairs you have a switch plate with two switches on it (two gang) one switch of which is for the upstairs light and one for some other light (possibly the downstairs hall).
You wish to operate the upstairs landing light from three separate places - one place downstairs and two places somewhere above? - Three-Way Switching - of one light.
To achieve three-way switching requires an Intermediate Switch (aka Changeover Switch) between two regular SPDT switches (Single Pole Double Throw - with Com, L1 & L2 terminals).
Here is a link to a Wikipedia article with drawings...
http://en.wikipedia.org/wiki/Multiway_switching
Be warned - the Red/Black colours in the diagrams DO NOT show Live & Neutral - Red Indicates a Possible Current Path and Black indicates No Current Path.
Also the designation 3 way and 4 way is American terminology indicating just the number of terminals on the switch.
My interpretation of your question may be wrong - if so - sorry.
I have no qualifications with respect to house wiring so my advice should not be relied upon.
If you are confused wait for a more sensible answer or engage the services of an electrician.
Good luck...Take care...
Peccavi
January 2010