During the 1870s, a grand scheme to build a network of narrow gauge railways throughout Snowdonia was proposed, Roberts being amongst those promoting the plan with Spooner being retained as engineer. The North Wales Narrow Gauge Railways Act of 1872 authorised the construction of a number of lines, of which the 'General Undertaking' authorised the construction of a railway between Betws-y-coed and the Croesor & Portmadoc Railway. Under the act, the tramway would be re-laid for use by locomotives at the expense of the NWNGR between the harbour and the junction with the NWNGR, at a point about halfway between Pont Croesor and Carreg Hylldrem, this work was not to commence until half of the connecting railway was completed. Unfortunately for the tramway the NWNGR's grand plans sank without trace, the General Undertaking being abandoned without any construction taking place, leaving the tramway to continue as before.
The only part of the NWNGR to be constructed was that from Dinas Junction near Caernarfon to Bryngwyn with a long branch to Snowdon Ranger (later extended to Rhyd Ddu). Whilst this was still under construction, Spooner tried to interest the Festiniog board in upgrading the tramway and then building a line from there to link up with the NWNGR, as with earlier overtures, the FR board were not interested.
The Portmadoc, Croesor & Beddgelert Tram Railway Company (BC&BTR) was incorporated by Act of Parliament in 1879 to absorb the powers of the Croesor & Portmadoc Railway Company and extend the line to Beddgelert. Roberts continued to be involved, but the remaining directors of the tramway left the scene. As before no progress was made with extending the line towards Beddgelert, and a further mortgage of £330 was given to James Cholmeley Russell on 19th June 1882, bringing the total borrowings to the maximum permitted in the 1865 act. The same year, Mary Elizabeth Littledale, principal creditor of the Croesor & Portmadoc Railway Co put the company into receivership, effectively ending hopes for the extension to Beddgelert.
The 5 years permitted for the construction of the Beddgelert extension would soon expire when Roberts, through Spooner, offered to build the extension on the undertaking that the Festiniog board would then purchase the completed line, yet again the FR board declined. A final offer was made to the FR in February 1883 that they should manage, equip and maintain the BC&BTR in perpetuity for an equal distribution of receipts. The offer was declined by the FR for a final time and so the tramway continued to go about its daily business quietly.