if you compare a 3.0d with a 3.0 petrol, is it really worth it?

considering that today the price of diesel is around 20% more....
and generally , at least in the UK you get taxed more for diesels...

so is it worth it????

or is the difference so small it really doesnt matter anymore??

i know if 4.4 petrol is more expensive to run than a 3.0d, but im talking about similar sized engines...