I dont think it has any to do with the valve seals since the engine in my car is rebuilt so I had to buy every seal new and the piston are also new.. Just recently I did 500km with my new engine but Im not using it right now because of that problem.
You say the fuel concumption has increased..... if this is the case the engine may be running very rich... I.E injecting too much fuel which subsequently isn't burning properly causing the excess smoke ( check out any old Ford with a carburettor and you'll see the excess smoke, although some burn oil too!)
The colour of the smoke is supposed to point to the problem:
White - water getting into the system, head gasket.
Black - excess or rich fuel, injection system
Blue - oil burnt, piston rings, cracked valves, etc.
yann what i ment was are you sure the work was done properly its very easy to break a piston ring when fitting it..you need to look at all your pipe work and make sure its all connnected properly.make sure the breather system isnt blocked.there is one other thing that will make a car smoke and that is a leaking brake master cylinder.!if the seals are worn fluid will leak into the servo and then be sucked into the engine from the servo pipe into the inlet manifold..from what you say about it only smoking when at the lights i would say its either piston rings/bores worn/or a stem seal missing or torn...but before that you must look at the pipe work and breather system.