How tight should my orbits be? I'm flying VFR circuits at a towered aerodrome, and the circuit is quite busy. With traffic ahead of me to land, the tower calls on the radio and asks me to orbit on downwind. I know it's good airmanship to keep a neat orbit, centred over one point on the ground, but how tight should I make it?

A tight orbit takes up less space (I've known there to be three aircraft all orbiting on downwind at once), but at the same time, it seems like a waste of effort and fuel to be making tight turns the whole time when the point of orbiting is to kill time. A lazy orbit (at say rate 1) would kill time just as effectively while flying at a much more comfortable attitude - and more stable in windy conditions.
It sounds like "orbit" is UK-speak for making a 360-degree turn for spacing in the pattern.  

I'm not sure what the custom is in the UK but in the US I was taught that you make a Rate One turn (3 degrees per second) for this, giving the tower two minutes between you and the aircraft in front of you (or the one on the ground they're trying to get rid of before you arrive).

The logic is that the maneuver is supposed to create spacing - flying a tighter circle takes less time, and thus creates less space between you and the aircraft in front of you. It also obviously requires more aggressive banking at low altitude compared to the relatively gentle bank required for a standard-rate turn at traffic pattern airspeeds, which as you noted will be easier to control in windy/gusty conditions.