I am pretty sure its fairly mild compared to your proper class As.
I always got the impression people basically sit around chewing it and shooting the breeze, like sharing a spliff with mates or popping down the local for a couple of pints. I hardly believe that that behaviour would be associated with a sleep-depriving, highly effective drug like speed.
Though having said that, i know some people do chew it all day long so perhaps they get really ramped up...
Wikipedia says - 'Khat is not a controlled substance in the United Kingdom. Because of this, and because of khat's short shelf life, the UK serves as a main gateway for khat being sent by air to North America.
Khat is used by members of the Somali and Yemeni community (mainly men), which is concentrated in London, Birmingham, Bristol, Cardiff, Manchester and Sheffield. It is currently legal, although there are calls from some sections of the Somali community for it to be banned. In the UK, Cathine and Cathinone are Class C drugs. The plant Catha edulis is uncontrolled.'