Help needed SR180 problems

[Dave1969]

Hi all, I have some problems with my 2007 SR180, and wondered if anyone has any suggestions, it's a bit long winded but here goes.
A few weeks ago I noticed what I initially thought was a flat spot, it's not when the engine is under load though, but when maintaining a steady speed, including when on cruise control, it's more of a judder/kangarooing feeling than a flat spot when it does it in the lower gears.
If I come off the gas it goes, and if I give it more gas it takes off perfectly like there's nothing wrong.
Then I noticed that it was smoking, it looks blue or white in colour and it does it when it's been sitting idling at a red light for example and I start moving again, it only emits the said smoke for a couple of seconds though then it stops, and although it does chuck out the odd puff of smoke on a motorway it's very very rare, it's mainly when round town.
I tried some injector cleaner in it and that just made it a whole lot worse until I got back to neat diesel.
It also started drinking loads of diesel, like 15 mpg around town, and about 24 mpg on a run, when it has always been around 30 and 38 respectively.
This was all according to the onboard computer, the fuel range would drop anywhere between say 8 and 12 miles when I'd only traveled 5 miles, like it was out of sync with what the car was actually doing.
I suspected the 5th injector was leaking/dribbling fuel so I replaced it with a brand new one today, then in the evening I did a 130 mile motorway round trip to test it and try to induce a regen, are they supposed to chuck out loads of black smoke when they regen, because I never saw any at all, only saw 1 puff of its usual blue or white smoke, and I was watching in the rear view mirror a lot because the road was empty.
The fuel consumption was back to 38 again on that run, but the flat spot and the smoking still persist.
I've had it MOT'd recently, and it had all these problems at the time, so I expected there to be a dpf or some kind of emissions problem, but it passed without a single advisory, and the emission result was 0, clean as a whistle, they didn't even have to purge/rev it at all which surprised me to say the least.
I borrowed an OBD fault code reader from a friend and it shows no fault codes, even took it for a run whilst that was plugged in with my friend monitoring it while I made it judder and smoke, and nothing showed up, there's also no lights up on the dashboard that there shouldn't be, and it's only used about a cup full of oil in the last 2000 miles.
I'd be extremely grateful of any advice or suggestions of any kind, as I'm scratching my head with these problems.