The DVLA are getting much tighter on vehicle mods. I read Practical classics and they are worried at how deep the DVLA are looking to dig into a cars history. There is even talk about MG's that have had heritage shells, not being able to claim road tax exemption, although a heritage shell is made using all original presses and tooling. Because the original shell is not used. The government, although granting tax exemption for vehicles over 40 years old, obviously don't want loads of people putting lots of old vehicles back on the road for free. So a lot of cars that have had engine swaps or so many new parts that it's almost a new car, may be in for some difficult times in the future, if these new DVLA plans go ahead.