PMSL.......
I've just read this post and couldn't believe the crap some people come out with.
No way is it illegal for you to use the engine for braking. As stated by a few people so far, i was also taught about slowing down using the gears. This was back in 1995.
For this dispute that you're having on another site, ask to see proof of this legal bumf that they're quoting, i wouldn't mind seeing a copy....... lol
As for there being no notice of you slowing down, as already stated by another good fellow on here, the 3rd party follwing behind should be leaving enough space between vehicles for any unforseen event i.e a dog running out on you in which case if he was following to close, would hit you anyway.
It sounds like he should be done for driving without due care and attention !!!! Not paying attention to was happening in front.
The fecking idiot !!!!!!