Elsewhere on the web it is stated that 1 pound in "late victorian" times was the equivilant to about $200 dollars today. Using the web site above to calculate inflation from 1770 to 1880 and then applying the $200/pound and converting back to pounds gives about 9359 pounds as being the equivilant of the 1770 amount of 40 pounds. a little fudging around with the year of "late victorian" can give as high as 11,000 pounds as the "today" equivilant of the 40 pounds.

I suspect in it would be much higher in actuality.