Define 'public'. If by 'public' you mean a large percentage of the population, the answer can be short, as the date falls after 1801. Possible dates include 1832, 1867, 1884, 1918, 1928, or 1969. If by it, you mean any part of the population (as opposed to formation of the legislature by appointment), there are different dates for England, Scotland, and Ireland.
In England, the Model Parliament was established in 1295 by Edward I (the greatest monarch of all time, as everyone knows). This unicameral legislature (separated in 1376) included members of the clergy and aristocracy, but, more importantly, 2 knights sent from each county and 2 burgesses sent from each borough. From 1430, the county electorates were standardised to include all people owning land on which £2 of land tax was paid (£2 being 40s, the term '40 shilling freehold' emerged). Thanks to inflation and economic growth, those electorate subsequently increased gradually over the next 400 years. However, boroughs were free to set their own rules; some boroughs allowed all freeholders to vote, others had wealth restrictions, others didn't allow any votes, and some had no inhabitants. Ironically, probably the most democratic were the university seats, which allowed all graduates of Cambridge of Oxford to vote.
In Scotland, it's far more messy, with the introduction of knights in dribs and drabs. Scottish representation was difficult to establish in the earlier years, due to the hazy constitutional situation, and ties to, and dominance by, the Kingdom of England. After Balliol's rebellion, representation was increased dramatically to cover burghs and territories in much the same way as England was represented.
Due to incomplete government (i.e. English) control, Ireland's parliament had very few powers (reflected in its decision, in 1494, to vote itself to become dependent upon the English Parliament). Its electorate included all non-Gaelicised freeholders in English lands, which, whilst making it the least democratic of the three bodies, made it the one that extended furthest down the social ladder.
Originally Posted by Humbird
Natalya, I think there already is an official "Ask Bastin" thread.
I demand stickiness!