Boundary commissioners today publish a second and final draft of how the country is to be carved up under plans to slash the number of MPs from 650 to 600.
Outrage followed the Boundary Commission for England last September creating a so-called "Devonwall" seat that includes Bude in North Cornwall and Bideford in West Devon.
Yet despite "overwhelming opposition" from MPs and councillors, the body said, officials say Government demands to make each seat the same size means a U-turn is impossible.
But they have adopted proposals put forward by the Conservatives to include two more wards in Torridge, Devon – but they say the revision will not "significantly alter the balance and nature of the constituency".
The Cornwall town of Launceston – the "ancient capital of Cornwall", the report says – will be included in the constituency's name so voters from "all areas can identify with it".
Elsewhere, a new Tavistock and Plympton seat in Devon has been revised to be more "Plymouth-facing" by ditching Okehampton on Dartmoor from the original proposals, and replacing it with Ivybridge.
However, the proposals are unlikely to go ahead, given Liberal Democrat opposition to the Tory-led boundary review.
Dan Rogerson, Lib Dem MP for North Cornwall, urged Westcountry Tory MPs to also vote against the change.
He said: "A cross-border seat makes no sense, and neither does a constituency that puts the Wadebridge and Padstow area together with St Austell.
"The Boundary Commission has ignored most of the sensible suggestions."
Some 18 Devon and Cornwall seats will be reduced to 17. Four constituencies are to be unchanged. Other notable changes from the current map include Hayle being assumed by the St Ives constituency and Truro and Falmouth separating.
Meanwhile, reports suggest a Tory "cash-for-seats" deal with the cash-strapped junior coalition party if the Lib Dems drop their opposition.
Lib Dem leader Nick Clegg vowed to block re-drawn boundaries in a House of Commons vote in revenge for rebel Tory backbenchers wrecking his plans for House of Lords reform.
However, senior Tories are hoping to contrive a U-turn in exchange for millions of pounds of state funding for Mr Clegg's party, with the review handing the Conservatives up to 20 extra seats at the next general election.
Stephen Gilbert, Lib Dem MP for St Austell and Newquay, said: "I am clear that I do not want to see a Parliamentary seat that crosses the Cornwall and Devon border.
"I am delighted that Nick Clegg has recently said that the entire Liberal Democrat Parliamentary Party will also no longer support these plans – they are a dead as a Dodo regardless of what some Conservatives may think."
