It depends on what kind of work you do, but it will not be a lot (I personally consider "a lot" as a more than 50% increase). 1050 is faster than 750 Ti roughly by 30%. May be not worthy of £40 premium. If 750 Ti is much cheaper for you, you'll be fine with it. Just look for 4GB version.
Ok. Last question, would the 1050 run 3d software like motionbuilder, Maya, Cinema4d, Unreal, etc a lot better than the 750? If it was £20 more expensive, I would go for it but it being £40 more expensive is just a little too much. If it will run 3d software a LOT better, then I might go for it. I don't game at all on my…