Well, no-one seems to be sure, including some boiler engineers I've spoken to, but here is what I've gleaned from other guys...
One chap has had his boiler running on purely contaminated fuel for the last 6 years

along with 3 friends' boilers too.
Another guy started, like the first, with a weak mix, then a little more, and so on, until he realised it was now on pure waste fuel.
Another one has it running on pure waste fuel and has done for over a year now.
Another 2 guys have just started to add it into their system.
So far, not a single one of them has needed to make any adjustments or changes to the boiler

Any more thoughts now?
My thinking is that as Kerosene is thinner than Diesel but thicker than petrol, my mixture is probably of a very similar viscosity. As Kevin has rightly said, Kerosene (or paraffin) are of very poor purity and often contain everything from the thicker oils to Avgas or even Jet-A1 (if it didn't meet the strict requirements), including Derv and petrol, so what have I got to lose?
