I'm intending to start running a car after it's been sitting in the drive for 2 years. Already asked a couple of questions in this thread. I've just noticed that not only is just about everything under the bonnet covered in dust, but there's some white stuff that looks similar to mould on top of the engine and around some of the pipes, especially near the connectors.

I'm guessing that it's not dangerous but will likely burn off and smell pretty awful as soon as the engine comes on and warms up. It looks like it would be very easy to wash off, so I'm inclined to basically throw a bit of water over it and wipe it down first. Can anyone confirm whether that is likely to be sensible?

It does look slightly powdery, but coolant leak seems unlikely because the water level in the radiator is still very full (besides some of the white stuff is on top of the engine - there doesn't seem to me any plausible way it could get there).

Unlikely in my opinion. OP- it's an old, low value car. Start the fker! You won't learn what's up until you try to get it to an MOT.

^^^ What Magpie says - it's the residue from aluminium corrosion caused by damp on bare ali.

I just bought a car which had its head and cam cover stored in the boot since '07, it looked like it snowed in there! (pics on request).

Don't wash it off, use a brush.

Use Vinegar and #00 wire wool then autosol to protect if you're that bothered.

The water splitter on the mother's fiesta was more corrosion than ally where there had been a very slight leak over time.