I suspect that they will start having some excuse for charging tax on EV as well as more people switch to EV's .Yes you are correct. Free before 1st April (mine too!).
now EVs are free. Otherwise its first year tax is based on CO2 emmissions then subsequent years are £140 for petrol/diesel and alternative fuel (includes hybrids) are £130
And if your car's list price is over £40k then you have to pay an extra £310 for the first 5 years.
same as congestion charge in LondonOf course! As soon as their income from car tax drops the rules will change! Thats why they changed them this time I am sure of it