Few things are more surprising in the history of London, than that a city which had grown to such magnitude and opulence, and extended for miles along both banks of a mighty stream, should, till so late a period as the middle of the last century, have had but one bridge across the river, that of London. (1824)

There were proposals in Parliament to build additional bridges at Westminster-Lambeth (1664,1721) and Fulham-Putney (1671) that were all rejected. The 1721 proposal was opposed by the City of London, the Company of Watermen, the West Country Bargemen, the Borough of Southwark, and the inhabitants of London Bridge.

The Watermen were operating their own water taxis and other privately-owned ferries, notably a ferry at Lambeth owned by the Archbishop of Canterbury. In 1720 at the time of John Strype's updated Survey of London (originally published in 1598) there were 40,000 Watermen on the Company's rolls, and they needed the business to not only support their own families but also Widows and Orphans as well. The Company were also expected to provide manpower for the Royal Navy, so maintaining a healthy number of Watermen in peacetime also served national interests. They were motivated by the direct competition from a bridge.

The Watermen were represented in Parliament by the City. The City also had a monopoly in London Bridge, but revenues from tolls (from carriages passing over and boats passing beneath), fines, and rents went to a subsidiary organisation (Bridge House Estates) to pay for maintenance. If bridge revenue was lost from competition then the City would be liable to make good any essential repairs. They were also representing the interests of small business owners whose livelihood derived from people crossing in that area (ditto Southwark) rather than other areas.

The Bargemen were opposed because the required piers for a bridge would impede their ability to navigate the river by creating collision hazards, and disrupting currents and tidal flows. A West Country barge was 12ft by 80ft and square sailed. They could sail underneath London Bridge because of its central drawbridge, but other bridges with closely separated piers required the use of poles (and additional crew). The Bargemen would also then be liable for any accidental damage to the bridge.

The Fulham-Putney bridge was a privately-funded toll bridge, authorised in 1726, opened in 1729, was 786ft long with 26 spans of various widths, and entirely made of wood. It was very prone to damage from aforementioned Bargemen and also drifting ice.

The Westminster-Lambeth bridge, when eventually authorised in 1736, made provision to compensate the ferrymen by £25,000, and compensate the Archbishop by £21,000. It was publicly funded and toll-free when it opened in 1750. It was built entirely of stone, with fifteen arches, and foundations laid in caissons; a very modern bridge. This was very important because as well as being more visually appealing the wider spans were less disrupting to river currents and river traffic. The testimonies of Bargemen to Parliament in consultation over the proposed bridge at Blackfriars a decade later make this point very specifically: that a new bridge to the same modern design as Westminster Bridge would be okay, whereas a new bridge to an older timber-based design would be a problem for them.

All important changes create winners (the general public) and losers (the Watermen and the ferry owners) so eventually the argument for additional bridges in the public interest overcame the opposition from vested interests.

The Journals of the House of Commons provide a record of contemporary testimonies; I'll try and post a link later.