Sir John Rennie visited Cuckfield on Friday last, and paid great attention to the work of the engineers, who are daily making rapid progress in order to satisfy the most fastidious that the line through Cuckfield is not only practicable, but superior to any other.
Indeed, so earnest is Sir John to overturn the assertions of Stephenson’s party, as to the unfavourableness of the soil for tunnelling, that he intends to cause shafts to be sunk, so as to convince them by occular demonstration that they have erred, and that the soil is every way favourable to the direct line.
West Kent Guardian (quoting Brighton Gazette) Saturday 16 April 1836
The precise route hadn't been finalised at this time. And may have been prompted by a meeting a month before, on 16 March 1836, with a House of Commons committee that was examining four routes. They were advised by Captain Robert Alderson of the Royal Engineers.
'He [Captain Alderson] recommended that a direct line, comprising portions of several different schemes, was the most suitable as the potential engineering difficulties could be overcome. Consequently the London and Brighton Railway Act was passed on 15 July 1837 authorising the London and Brighton Railway Company to construct a direct route with branches to both Shoreham and Newhaven.'
Construction and opening
'Construction of the new line commenced on 19 March 1838 under Sir John Rennie and John Rastrick, and was undertaken by a total of 6,206 men, 960 horses and 5 locomotives.
The first track was laid at Hassocks in February 1839, but it was to be another thirty months, on 12 July 1841, before the line opened, and then only from London to Haywards Heath with a connecting coach service to Brighton.
The line opened to Brighton itself on 21 September 1841; the first train set out for the City at 7 am, and the first down train arrived in the town at 2pm amid scenes of great celebration.'
From My Brighton and Hove website: https://www.mybrightonandhove.org.uk/topics/topictrans/railways/railways-5
Blue plaque unveiling: https://www.haywardsheath.gov.uk/_VirDir/CoreContents/News/Display.aspx?id=26916 Located at 1 Muster Green.
Contributed by Malcolm Davison.