What were British voting qualifications in the 1770's?

The country was divided into counties and boroughs.

To vote for county MPs (usually two per county) a man had to own freehold property worth forty shillings per year. This means that it could be let for that amount. Whether it was, in fact, let was irrelevant.

Most boroughs also returned two members. The qualification for voting varied from borough to borough.

The most democratic were known as "pot walloper" boroughs. In these any man who was able to boil a pot in the town, that is anyone who had his own hearth, was entitled to vote. In such boroughs the form of tenure was irrelevant.

Some boroughs used the "scot and lot" system. This meant that only those who paid certain church and poor relief taxes could vote. The obligation to pay these taxes was often linked to membership of merchant guilds, which in turn gave people the right to trade or carry on certain occupations within the town. In effect, those with the right to traded or do business in the town were able to vote.

In some boroughs the "burgage" system was used. This meant that anyone who held property in the town on a yearly rental, either directly from the king or from a specified local lord (depending on the borough), was entitled to vote. The holder of such property might or might not personally reside there. The property could be sublet, and the right to vote might be let with it, let separately, or retained.

The least democratic were boroughs where the "corporation" method was used. In these boroughs the right to vote was held by members of the corporation, which in many cases was self-perpetuating, with new members being appointed by existing ones. In many cases the corporation was responsible for aspects of the town's administration, but in some there was no town, merely a self-perpetuating group with the right to elect two MPs - these included the Rotten boroughs.

Another system involved "freemen" of a town having the right to vote. In some cases freedom of a town was inherited, or granted automatically to apprentices, and/or at the discretion of the corporation. There were instances of large numbers of new freemen being created just in time for elections.

In many cases a man otherwise qualified to vote could not do so if he was in receipt of poor relief. Generally, only adult male Protestant British subjects could vote.

Not everyone who had the right to vote had the opportunity, at least not often. Very many MPs were returned unopposed. Nobody might choose to stand against the nominee of the major landowner. In other areas once an MP was elected to one Parliament, if he wished to continue he might be elected unopposed to successive parliaments until he chose to retire, or gave cause for significant dissatisfaction. Local convention could be important, for example Lancashire county traditionally elected one member of the Stanley family, and one other. Where elections were contested they could be the cause of very great excitement. To vote people had to attend the county town in person and might at the very least expect to be reimbursed their expenses by whichever candidate they voted for.

Strictly speaking, Birmingham and Manchester were represented as part of Warwickshire and Lancashire respectively, and in the late eighteenth and early nineteenth century Warwickshire conventionally sent one MP from Birmingham and one other. Lancashire sent two county members and two each from Liverpool, Lancaster, Preston and Wigan, but none specifically from Manchester.

This paper, from the House of Commons library, goes into more detail.

As Steve Bird has stated around 3% of the population could vote, which if we exclude women and boys is perhaps close to 10% of the adult male population. The proportion fell somewhat during the eighteenth and early nineteenth century as the general population increased faster than the voting population.