Thanks for all the replies - some very interesting discussions. Obviously we are not in a position to risk blowing a chunk of our budget on something that won't work - though this could be true of both brushed and brushless. I will come back to you once we have more info on the drive system. It currently looks like it will be chain driven (ratio of 3:1 assuming a rough rpm of 3000rpm from the motor) with a torque limiting clutch in between. The current design looks to be unsuitable for a belt drive - partly because we can't find belts small enough and also we would want two belts and are limited with the depth of the gearbox.

We have another robot on the go which we plan to use for combat practice. There will be space for a spinning drum so maybe could look into brushless on here as this is more experimental.

I noticed on eBay you can buy a scooter motor and controller (brushless) for not a huge amount. I wondered whether the controller would be a simple case of connecting the throttle wires together to get it to run. If so this might be an easy thing to implement.

Thanks!