Depends on the roads in question, but I'd be more worried about being tail-ended by some idiot hooning round a corner on a minor road than most dual-carriageway I've used.

Must admit I'd stay off the A3 much of it's more like a motorway, tho' I *have* seen cyclists on it just south of the M25 junction at Wisley – there's even a recommended suicide route shown on how to cross the M25>A3 sliproad, but there *is* still the problem of how to negotiate crossing the A3>M25 sliproad without some idiot taking you out..