This is by far the best explanation I have got with regards to the road tax applying to Alphards and Vellfires (or you can say most Japanese Imports). This is from a DVLA agent I chatted with earlier. Hope this helps others wanting to find out the reasoning. So it basically does not matter whether its a 3L V6 or a 2.4 petrol or 2.4 Petrol Hybrid. Tax is the same for all due to following reasons:
To find out the current exact rates, you can go to this URL and find out:
https://www.gov.uk/vehicle-tax-rate-tables/other-vehicle-tax-rates
Still don't know why would the govt charge same for a normal and Hybrid vehicle. Just a way to make more money I guess.