The Pembroke and Tenby Act of 17 July 1864 authorised a standard gauge extension from Tenby to Whitland, and also a standard gauge west curve at Carmarthen, allowing through-running from Whitland into Carmarthen Town and to meet the Manchester and Milford Railway. It was assumed that the GWR would lay a third rail, making their tracks mixed gauge, to carry standard gauge trains as well, from Whitland to the west curve at Carmarthen. Capital for the Whitland extension was set at £200,000.