Mick, this bit is wrong
Bear right at a roundabout under a footbridge still on the A396, and right at the next one onto a minor road past Blundell’s School (posh private skool) and go through Harberton and Sampford Peverell to the A361 dual carriageway. You cross this road over a flyover and sort of cloverleaf and wind back on yourself.
The road is fast and busy, but wide, and before you get off the slipway, you can ride along a layby, and by the time you get to the end of it, you reach a busy roundabout. Total distance on the dual carriageway A361 is only half a mile.
Head straight across the roundabout. It’s a bit fast, but it’s fine if you get a move on. If you have difficulty, get off and cross the road on foot. It’s the M5 Junction 27, so can be a bit hectic.
Straight on is what you want, and it’s the A38. Not too busy because the big traffic is on the M5. Head north for Wellington and turn off through the town centre as it’s the easiest route.
In Halberton turn right sp Willand - there's a pub on the junction
Follow that road to a "straight over rbt", under the M5 and past a chippy
Now, at the next RBT (which has a Coop that's open to 11pm on it) there are two choices
. 2nd exit, up to next RBT (Waterloo X) then 3rd exit to go on A38 towards Taunton/Wellington. Don't go through Wellington town centre, take the 2nd exit sp Taunton/M5
3rd exit, sp Uffculme. In Uffculme follow the road and you will cross the river. Keep to that road and you will go through Culmstock. After Culmstock climb the hill and at the top take 1st R then R at T. Through Nicholashane and a notably muddy dip near a farm, cross the M5 AGAIN and descent to R at T and onto the Wellington Bypass. Do not go through Wellington unless you love waiting at traffic lights (or want to visit Waitrose)
Choice 1 is better if it is rainy or if you want to ride very very fast
Choice 2 is better if you want an easier route (It's the Blackdown Hills neither route is flat)
Between Wellington and Taunton there is Sheppy's cider factory outlet. Just saying.
At the other end of the bypass there are a load of RBT, just keep following sp to Taunton and then follow Mick's suggestion of going through Taunton. Which is not a great experience