Short answers, pulled from the story.
Robert Wallace initiated the campaign for cheap postage by speaking before a governmental commission in 1835. He claimed that greater use of the mailing system would actually increase revenue for the government instead of reducing it.
Rowland Hill expounded his concept for reformed service at a meeting of the commission on the 13th of February 1837. He published a famous pamphlet titled Post Office Reform: its Importance and Practicability later that same year while serving as secretary of the South Australian Colonization Commission.
The Post Office (Duties) Act 1840 passed into law with the citation 3 & 4 Vict. c. 96. This legislation legally established the Uniform Penny Post across the United Kingdom of Great Britain and Ireland.
It would appear that the cost to an established semi-skilled man of sending a letter in 1840 can be represented by approximately £1 in 2013 values. The value of one penny in 1840 ranged from 32p to £4.89 depending on income calculations.
In 1840 the number of letters sent in the UK more than doubled immediately after implementation yet financial losses occurred during the first year. Financial losses gave way to massive increases in letter volume within the first decade of operation as Hill predicted cheaper letters would increase profits.