Creating a constituency which involves crossing of the Tamar, the river separating Devon and Cornwall, is where much of it lies. Cornwall is really a separate nation in its own right, with its own language, own history, and own culture, and this extends to the people of Cornwall in comparison to the people of Devon, where close links have nevertheless persisted since time immemorial. Sadly, under current parameters and electorate numbers, it is unavoidable without special legislation protecting Cornwall's cultural identity, which should have been in the original act given Cornwall's status within the Framework Convention for the Protection of National Minorities. In fact, the Cornish (who like the Welsh, Scots, and Irish, are Celtic in origin) are rightly recognised as a distinct minority in the UK: https://www.gov.uk/government/news/cornish-granted-minority-status-within-the-uk
All that can be done at the moment with respect to the 2018 Boundary Review is to make sure as little of Cornwall as is practicable is contained within a Devonian constituency; this should be (a tweaked version of the initial proposal of) Bideford, Bude & Launceston. Elsewhere within Cornwall, restoring old pre-2010 boundaries is much more prudent than creating new Cornish constituencies with poor connections to each other. Recreating Bodmin, Truro (& St Austell, a town now too large to be not recognised within a constituency name) and Camborne & Falmouth is therefore the way to go.
Rural Devon and the city of Plymouth are more complex in terms of new boundaries. Plymouth is too large for two seats but also too small for three seats, so inevitably one set of suburbs will have to be joined in a Tavistock constituency. Central Devon is also awkward because of its poor road links and by being under-quota; it was only created to give Devon the extra seat it was entitled to the last time constituency boundaries were changed. It is well worth noting that Tiverton and Honiton should be separated in constituency terms, because Tiverton and Honiton have no proper connection to each other except via Exeter, and in fact never really did which is why the constituency did not exist until 1997; it was only joined when the old constituency of Honiton grew too large. The major problem is that Tiverton is best linked with South Molton, the southern part of the North Devon constituency which should remain unchanged due to its own strong links with Barnstaple; in any case, a hypothetical constituency stretching from Ilfracombe to Bude via Barnstaple and Bideford (Bideford was briefly part of the North Devon constituency from 1974 to 1983) would be too large. Therefore, attaching Tiverton to much of Central Devon (as was the case previously) is the best solution to this problem, as is recreating the Honiton constituency (minus Exmouth). My proposal for Exmouth, however awkward it may look, does at least have some links to villages in between by means of the M5 motorway and associated roads, and surrounds Exeter to which it has strong links with. This also avoids disrupting general links that Totnes and Newton Abbot have.
My alternative constituencies for Devon and Cornwall thus look like this:
Honiton succeeds Tiverton & Honiton.
Exmouth succeeds East Devon in practice despite looking very different from the current East Devon.
Tiverton succeeds Central Devon in practice; Tiverton was connected to much of it (though not Okehampton) previously in constituency terms.
Tavistock succeeds South West Devon.
Plymouth West succeeds Plymouth Moor View.
Plymouth East succeeds Plymouth Sutton & Devonport.
Bideford, Bude & Launceston succeeds Torridge & West Devon; this is the unfortunate cross-Tamar seat.
Bodmin succeeds South East Cornwall, just as it preceded it.
Truro & St Austell succeeds St Austell & Newquay in practice, even though it recreates the old Truro constituency.
Falmouth & Camborne succeeds Camborne & Redruth and recreates the old constituency of the same name.
Torquay & Paignton has the same boundaries as the current Torbay constituency. The name has been adopted to reflect what the two largest towns in this constituency actually are, and to reflect that a significant part of Torbay council (Brixham) is in the Totnes constituency and will continue to be.
North Devon and Exeter are both unchanged.
Newquay & Wadebridge is a new seat and is similar to the old boundaries of North Cornwall minus of course the Bude and Launceston of Bideford, Bude & Launceston.
Next in this series: Wiltshire & Dorset.