[Discovery Gross Vehicle Weight Or MAM GVW Etc]

as far as I can work out:

You can tow a trailer up to 750KG providing the MAM of the train doesn't exceed 3500KG

You can tow a trailer over 750KG providing the MAM of the train doesn't exceed 3500KG and the MAM of the Trailer doesn't exceed the Unladen weight of the Tow Car

Yes I beleive that is correct for overrun brakes. If the weight of the trailer is greater than the car it says you must have couppled brakes not overrun which I assume is something like the air brakes that are on HGV trailers?

[Discovery Gross Vehicle Weight Or MAM GVW Etc]

I took the part E test back in 2004. Its mostly common sence. I couldn't afford a £600 course so thought I just have a go at taking the test after a bit of practise with my dad's help. Test cost around £80 and I failed it the first time so it cost me £160 all in. I managed to find the examiners hand book on the net so I knew what standard was expected etc.

[Running on waste engine oil]

On the legal side, you are only exempt from paying duty on non-hydrocabon fuels such as veg oil. Engine oil would be subject to duty in the same way that you would have to pay duty if you run on heating oil.

[IIRC]

IIRC, it means If I Recall Correctly