Just been watching some indoor trials action on M&M and wondered why they use knobbly tyres? If they indoors wouoldnt it be better to use some really, really soft compound slicks?

it's prolly something to do with a regulation about trials riding burried back in the anuls of time, something to do with an unfair advantage or something

Slicks wouldn't be much good going up that waterfall they use. Slicks also tend to work best with a bit of heat in them. You don't get much heat in a tyre with short bursts of speed and bouncing up and down moving the bike around.

i know they also run feck all tyre pressures in those trials about 5-10 psi i think

Flat tyres, reduced pressures, rubber grip stuff on the obstacles? How about cut slicks then!