David Cameron has been speaking to ITV Border's Scotland Political Editor Peter MacMahon at the Scottish Conservative Party conference.
When asked whether there would be border controls between Scotland and England this was Mr Cameron's response.
More top news
No trains will be running between Carlisle, and Edinburgh and Glasgow Central.
All Northern services at Carlisle station will be affected by the strikes, and replacement buses are in operation.
An earthquake measuring 1.7 on the Richter scale has been recorded in Cumbria.