Per [2] a furlong is 220 yards and a yard is exactly 0.9144 m.
Per [3] a fortnight is 14 days.
As I didn't find a good authority for what definition of a day a fortnight is
measured in, I'll assume here a day is 86400 SI seconds.
Thus, the speed of light in a vaccum is approximately
1.80*10^12 furlongs per fortnight.
1.80*10^12 = 299792458*86400*14/(220*0.9144)
[1] Resolution 1 of the 17th meeting of the CGPM (1983)
http://www.bipm.org/en/CGPM/db/17/1/
[2] Weights and Measures Act 1985
http://www.legislation.gov.uk/ukpga/1985/72
[3] The Concise Oxford Dictionary, 5th Edition, 1964, p. 480