Another vote for Anu… Autosol. It doesn’t need much, and even with a soft cloth will get it shiny in no time.
In terms of overfuelling, you could get the injectors checked, but unless you have noticed an MPG decline it’s unlikely on a standard car, or replace plugs if old, but you start to go down a rabbit hole. I’d just enjoy it and clean the pipes on occasion!
Probably needs a good thrashing whilst also introducing super unleaded into the system. I run mine on the E5 and it definitely runs better, smoother than the E10.
Yes, green scouring pads will scratch not only chrome but glass too.
White should be ok though.
OK, so I squirted a can of Wynn’s EGR / Air Intake / MAF Sensor / Inlet Valve Cleaner into the intake and put a bottle of Wynns Xtreme Petrol System Clean in the tank and did an accurate measurement which came out at 36 MPG which was mixed cross country & town driving, without holding back on the beans once in a while.
Exhaust pipe still has a very slight coating of soot after a run; not the clean grey of Richard’s pic but as far as I can detect, the exhaust gas does smell cleaner.
I haven’t looked at plugs yet. Will do that tomorrow. Watching the Torque app as well as I can while driving, commanded and measured air/fuel ratio seem to track pretty accurately. (AFR(c) & AFR(m))
Interestingly, I previously had a bit of a burble from the exhaust when heading downhill with foot off the accelerator but this has now gone. (Shame, 'cos I quite liked it :¬)
All in all I think this is an improvement and I’m sure I could improve on the 36MPG with a lighter right foot. (But where’s the fun in that 
)
Edit - Looking back at this thread it looks like Richard’s suggestion of a dirty MAF was the most likely cause here.