Definitely not breaking any rules.
Regarding "fairfuel", both petrol and diesel have the same tax at 58p per litre. The reason why the pump price of diesel is higher than petrol is because the cost of diesel is higher before the tax is added on. Although the prices may have changed since 2011, the picture below is basically unchanged because the fuel duty is the same.
I'm not sure what additive you're talking about, you might be confusing bio-diesel with Adblue.
As far as I am aware, the only way that diesels can get through the latest Euro 6 emission standard is by using Adblue. This is added from a tank into the exhaust stream to reduce most of the NOx back to Nitrogen and water.
The 7th and 8th gen Accord diesels do not have an Adblue system so, based on current trends, they are likely to be banned from cities in the future.
The problem with the diesel engine is that it is a lean-burn engine (oxygen rich), and if you burn anything carbon based in too much oxygen (e.g. a bonfire) then you get NOx produced. NOx has always been the most harmful product from combustion, and it seems that the VW scandal served to highlight to the public something that was already known to environmentalists, which is that the diesel engine in too many cars and vans in urban environments produces too much NOx in the streets where people are walking (and the buildings where they live or work).
The reason why diesel-engined cars and vans were being "promoted" as green was because they are more efficient than petrol engines (mainly because of higher compression ratio and lower pumping losses). Thus their CO2 output per mile is less, the penalty for which is particulates and NOx .
Diesel cars have only really been popular in Europe because of the better mpg, and because of the reduced CO2. It wasn't any UK government that was pushing the diesel, it was a cultural phenomenon based on those facts, and the emissions standards were too slow in forcing the diesel engines to use equipment to reduce the particulates and the NOx.
If the Euro 6 standards had been introduced say 10 years ago, then I doubt whether Honda would have bothered, they only really introduced diesel engines to keep market share where other marques had diesels, indeed most of the equipment on diesel cars is Bosch.
So there wasn't misinformation as such, it's just the slow process by which emission standards came into place in the EU, such that there was a period that allowed diesel engines on cars and vans that should never have been allowed in the first place.
On the bonus side, you may have a diesel scrappage to look forward to