The presumption that the Great Western Railway would acquiesce in mixing the gauge of the track from Whitland to Carmarthen proved to be naive; the GWR would not hasten to facilitate unwelcome competition in its own back yard. This difficulty came to light during the construction of the Whitland extension, and the Pembroke and Tenby directors decided on 12 October 1865 to survey an independent line from Whitland to Carmarthen. The line was to be 14 miles long, running generally south of the GWR line but crossing it at Sarnau.