1)Valiant Central Heating Boiler with metal flue going through ext brick wall.
a)contractor has drilled a hole in the brick wall for flue,fitted
valiant boiler to wall,connected flue with flue terminating ext wall
THEN filled all existing (appox 10-15mm)space IN & AROUND and ON top off
METAL flue with WET cement motar so that the part off the metal flue
in the wall has been completly encased in WET cement motar;
Q)Is this correct as I asked should we not keep wet CEMENT away from
metal and should flue be allowed to move when it gets HOT;CONTRACTOR
STATED NO,fitted a rubber flange on outside wall and left.

Let me get this straight, where is the bolier located?  

Basically your inquiry is questioning the integrity of the boliers
flue because it was encased in cement - correct?

If this is the case then you don't have anything to worry about -
thermal expansion of the flue will still take place.  Most flue pipes
have to be "double wall" which is basically a "pipe within a pipe" and
this is to help ensure a safe source for exhausting posionous fumes to
he exterior of a dwelling structure.  The only way you might a problem
would be if he placed motar in the flue reducing the circumfrence
available for exhausting fumes.  Other than that you have nothing to
worry about.