Sorry, it's me being a blind as a bat
Though you did only mention M27, it would go on two other motorways however short they are
Of course a lot of the journey won't even be on dual carriageways, yes the A38 and the A30 will all be on dual carriageway sections (the A30 dueling ending around Honiton) but very little of the A35 it uses is duelled (we are talking probably less than 5 miles) so that really only leaves the Upton Bypass, the small section on the A352 (a dual carriage way on a minor A road!, though only about a mile) and the A338 Bournemouth Spur Road in Dorset.