A remap will actually improve the efficiency of a standard engine.
I noticed my Mercedes Smart Cdi diesel felt far happier on the road, after its remap, and increasing the hp from 62hp to 78hp saw improved fuel efficiency.
I did not quite manage 100mpg from it, but could reach the other side of 90mpg on long motorway journey's.
When you tune an engine with a Stage 1 remap, the engine is tuned to close its optimum level and efficiency.
After its remap, the engines new lease on life, can become more efficient than when it leaves the factory, simply because the engine has been retuned to optimum efficiency.
When it leaves the factory, the engine is in a detuned form, to take into consideration the inferior fuel found in other countries where the car is sold.
The remap should provide increased power and torque figures right across the rev range, and allowing the engine to increase its fuel efficiency if driven with all out fuel efficiency in mind.
On a journey to South Wales several weeks ago, travelling through Mid Wales along the A470, in my Move Up, i averaged just slightly under 75mpg.
I know we can take the Maps & More fuel efficiency programme with a pinch of salt, but when i filled the fuel tank to the brim, the fuel needle did not start to move until 184 miles, and for a short distance outside Builth Wells, it was showing i was doing 80mpg.
I just cannot understand why your Up! is only returning 45mpg?
Even in normal driving, ive never seen less than 60mpg from my 59hp engine.
The 75mpg was achieved when i adopted a fully focussed driving style, and i always use Tescos Momentum 99ron fuel.
The 1 Litre engine is supposed to be very fuel efficient, so averaging 45mph seems rather poor.