The changes would have coined it in to the tune of £7m
A council's claim it aimed to raise parking fees solely to cut congestion has been thrown into further doubt after a BBC investigation found it carried out detailed costings to assess how much money it could raise.
Westminster Council - which already makes more from parking than any other London borough - is proposing to charge drivers to park in central London until midnight.
It argues other less-congested boroughs have extended their parking controls and said the authority aims to balance the interests of residents and visitors to Westminster.
But BBC London has now seen a document prepared by a council officer showing they expected to make almost £6m-a-year from the plan.
A raft of other proposed measures, such as "harmonising" pay and display costs in St John's Wood by doubling the price, would have netted nearly £2m more annually.
The council's prediction for how much money it would raise was set out in a detailed table circulated internally - but not added to a publicly-available document.
Using parking to raise revenue is illegal, following a 1995 High Court judgement.
Councils are, however, allowed to make money if revenue is "incidental" to other motives, such as keeping traffic moving.
On Wednesday, Councillor Danny Chalkley, cabinet member for city management, insisted it was "not correct" the proposals were intended to raise money.
He maintained the council's sole objective was to protect limited kerb-space.
Then BBC London obtained a briefing document, dated a week before Mr Chalkley's comments, showing council officers were ordered to "go away and look more closely at parking to find additional income".
The briefing made clear parking was "earmarked" as a way of finding money to reduce the council's £22m overspend.
WHAT WESTMINSTER EXPECTED TO MAKE
£5,881,500 from charging to park until midnight
£783,000 from "harmonising tariffs" - doubling the cost of parking in St John's Wood
£432,000 from "harmonising" pay-and-display parking in inner zones with similar bays in Camden
£275,000 from increasing residents' permit costs
£293,000 from increasing the tariff for suspensions
Campaigner Paul Pearson, who runs parking website penaltychargenotice.co.uk, said the document completely undermines the council's claims.
"Westminster claimed it was nothing to do with raising money - yet they costed it out in pounds, shillings and pence to see exactly how much they would make," he said.
"I find Councillor Chalkley's public comments incredible - he knew officers had been asked to look at parking to find extra revenue.
"For him to insist it was nothing to do with raising revenue is astonishing."
The total amount the council stood to make was equivalent to a third of their budget overspend.
Mr Pearson added: "I find it simply unbelievable that councillors were not aware of the briefing [which ordered officers to make extra revenue from parking to address the £22m black hole].
"Officers were told to go away and come up with ideas to raise revenue - this was the idea."
'Open to scrutiny'
However, Kevin Goad, Westminster's head of commissioning for city management, said other authorities have acted in similar ways.
"A number of other local authorities in far less congested areas have extended parking controls," he said.
"But we are listening to those affected and will consult on what are just proposals.
"We constantly try to balance the interests of businesses, residents and motorists and our final decision will be made in a manner totally transparent and open to scrutiny."