CC
I had to phone up for that price as a 25 kg sack wasn't on the inventory. I don't recall a single kilo being quite as much as £2, either, but I might be wrong.
The colour range of Imperial is 40-50 ebc while even dark Munich is only 25. Moreover, it's tastes more like an amber malt, even though it's lighter. I don't know whether you could get away with using one third of the amount of Munich called for in a recipe; it would taste nice, but it would be different, I think. Also, I suspect Imperial is made from Pale Ale malt while Munich is made from Pilsner, so even if they were both roast to the same colour, I would expect the Imperial to be "maltier".