I've been trying to work out roughly what happened - or mostly didn't - to this railway.
The Preston and Longridge line was opened in 1840, as a single line worked by horses uphill and carrying stone from the quarry down Preston by gravity. That quarry traffic was attractive, more so if it could be expanded by steam operation and better linked to railways and docks.
The original Fleetwood, Preston and West Riding Junction Railway proposal was to go from Preston to Elslack, joining the Leeds and Bradford extension Railway for the onward route via Skipton. That started from the Preston & Wyre line, and included taking over the P&L in its first stage. There was to be a branch from Mitton to Burnley, via Whalley and Padiham.
At least seven companies were vying for the right to build railways through Clitheroe, of which the Blackburn, Clitheroe, and North Western Junction Railway proposed an almost identical route for Clitheroe-Skipton and a branch to Burnley. The result of the horse-trading was that the FPWRJR was only to "build" the 16 miles Preston-Clitheroe, and gave up the Burnley branch which was then not pursued by the BCNWJR either. This act was passed in 1846.
The link line through Preston (including the tunnel) was built, about a mile in all, by 1849/50. While the FPWRJR was granted the right to buy the Preston and Langridge, the agreement they reached was to pay £3000 pa for 24 years. But in 1856 they fell out about the terms, and ended up completing the purchase outright. There was a financial regulation act for the FPWRJR that year.
I am not sure why the next part of the line to Clitheroe was not built. It just isn't mentioned in reports of company meetings. At the same time they were still trying to get a further bill through Parliament, for the "Burnley and Colliery Branch" (from Mitton).
A new bill was promoted in 1865/6, with short numbered railways running:
1. Fulwood (on the Preston-Longridge) to Standen via Grimsargh, Ribchester, Mitton, Pendelton
2. Standen to Chatburn
3. Chatburn to Elslack
6. Little Mitton (on no. 1) to Whalley
That bill was debated in March 1866, and then in August the LNWR and the L&Y bought the whole railway.