... is it as simple as it looks, i.e. un-do the bolts which go through the bushes and simply replace?

How long should a garage be able to do it in? 1/2 hour?

Would have thought a garage would take an hour, only takes me about an hour and a half working at a very slack pace.

Here's how I do it:

Slacken wheel nuts and driveshaft nut

Jack and axle stand on that corner.

Remove road wheel

Undo pinch bolt

Rattle a big flat screwdriver in the pinch to slack it off a bit

Optional, but I find it helps, remove driveshaft nut

Put a long bar over the bottom arm and under the chassis leg, jump on said bar to pop the ball joint out of the pinch in the strut

Shove strut out of the way

Optional, slacken that ARB mount at front (I don't normally take them right off, it just gives you some more play when putting it all back)

Remove ARB nut

Remove inner bush nut and bolt and arm out of mounting

Batter arm off ARB with a whammer.

Put new arm on arb, spin the nut on a couple of turns so you've still got play in it while you line the rest up.

Put the inner in the chassis mount, pop the bolt in, but as before, spin the nut on a couple of turns so you've still got play in it while you line the rest up.

Grease the ball joint so it slides out easier next time

Locate in bottom of strut (I have been known to have to push this back in with a trolley jack. If you're doing this, make sure the axle stand will catch the car if things go Pete Tong).

Locate pinch bolt and tighten.

Tighten ARB nut, inner nut and bolt, front ARB bolts.

Got for a tea

Idiot check above nuts and bolts for tightness

Replace/renew driveshaft nut

Replace road wheel and studs

Lower car

Tighten road wheel studs and driveshaft nut

Thanks for the detailed guide :)

Would the suspension arm or bushes be responsible for the occasional 'clunk' sound which i get when going over bumps?

(I have changed the top mount and it is not that, and the car did pass its MOT the other day hence wouldn't they have commemnted on the bushes?)

Yes, very much so.