The actual location that will be used remains uncertain, with a number of venues - both near and further away from Tokyo - under consideration.

According to a senior International Olympic Committee (IOC) source, the original Wakasu Olympic Marina, priced in the bid book at $105 million (£69 million/€97 million), would in fact have entailed construction of a breakwater costing more than $400 million (£263 million/€368 million).

This requirement could have been removed by switching the venue inland to an existing sailing centre not far from Wakasu.

However, this gave rise to another issue, since live coverage of sailing entails the use of helicopters which would require clearance from authorities at Tokyo’s Haneda Airport.

It is still not clear if permission can be obtained.

The IOC source also confirmed that original plans for a temporary velodrome, priced in the bid book, along with a BMX course, at $74 million (£49 million/€68 million), would be changed, with possible alternative options including adaptation of a keirin venue.

Water polo may also be moved.

It looks, meanwhile, as though badminton may well go to Musashino, although this is understood to be subject to final approval by the Badminton World Federation.

These new details of revised plans for Tokyo 2020 emerged as the IOC spelt out how the estimated $1 billion (£658 million/€919 million) of savings already identified would be achieved.

The vast majority is derived from scrapping the Youth Plaza project that was to have housed both badminton and basketball.

While the Tokyo 2020 bid book put the overall cost including overlay at $420 million (£277 million/€386 million), the IOC source said this had since been revised up to $880 million (£579 million/€809 million).

As previously announced, basketball is to be moved outside Tokyo to Saitama’s 37,000 Super Arena, the venue for the 2006 men’s World Championship.

The search is understood to be on for a second basketball venue close to Saitama.

If badminton does go to Musashino, the IOC source indicated, costs incurred for all three venues would be fit-out costs only.

The other approximately $100 million (£66 million/€92 million) of net savings already secured comes from the switch of some equestrian events from Dream Island to Baji Park, a venue from the city’s 1964 Olympics, the last time the Japanese capital hosted the Games, which is located about 50 minutes from central Tokyo.

The IOC source explained that Baji Park belongs to the Japan Equestrian Sports Association which is a private entity.

This body is said to be willing to pay the cost of any renovation work required.

The $1 billion (£658 million/€919 million) does not, however, include any contribution from the rowing/canoeing venue at Sea Forest, which has been left in situ after substantial revisions to earlier plans.

The IOC source explained how the original bid-book cost of $78 million (£51 million/€71 million), plus $23 million (£15 million/€21 million) for overlay was threatening to spiral above $1 billion (£658 million/€919 million) because of demolition work and the relocation of bridges that was said to be required.

Extensive design optimisation work is said to have cut this price tag to $490 million (£323 million/€451 million).

Of this, the budget for the two sports is said to be less than $100 million (£66 million/€92 million), with municipal authorities contributing the remaining $400 million (£263 million/€368 million).

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