The need for an £80bn hub airport in the Thames Estuary has been challenged in a report claiming existing London airports are not being used effectively.

The report has been prepared by an influential cross-party transport committee of members of the London Assembly.

It says millions more passengers could use Heathrow, Gatwick and Stansted if larger aircraft were used and emtpy runway slots were taken up.

It questions the case for a new airport, saying it is not viable on grounds of cost, damage to the environment and disruption.

The conclusions represent a major challenge to London Mayor Boris Johnson, who has argued the UK is falling behind emerging economies because of a lack of aviation capacity.

The committee says it is not convinced by that argument and suggests growing demand could be met if better use was made of existing airports and passengers were able to fly in larger “hub buster” planes such as the new Airbus 380.

It also calls for improved road and rail transport links between airports but rules out any further expansion of Heathrow.

The committee says research it commissioned showed that while Heathrow was operating close to capacity, 20 million more passengers could use it if larger aircraft were routinely used.

In addition, it found that at Stansted Airport, nearly half of all runway slots are available while at Gatwick, 12 per cent are unused. At Luton Airport, more than half of runway slots are not being used.

In a key conclusion, the report says: “The case for increasing airport capacity is not clear cut. The economic importance of providing more airport capacity is disputed and a key economic consideration is local demand for air travel.”

It says it is not obvious passengers would automatically use a new Thames Estuary airport if services were still being run from others, including Heathrow.

“It would appear some options such as building a new runway at Gatwick and/or Stansted are more viable than building a new airport in the Thames Estuary.”

“If the importance of a competitive hub is overstated, then an approach of using existing airports more smartly could be more cost effective than building new runways or airports.”

Caroline Pidgeon, chairman of the London Assembly transport committee, said:

“Evidence we received shows the Airport Commission [set up by the government] must examine whether better use of existing airport capacity could be an intelligent cost-effective alternative to building new airports or runways.”

She added: “The need for additional hub capacity is also under debate, with strong data showing rather than runway capacity limiting airlines ability to fly to emerging markets, it could be low passenger demand from each airport’s geographical area. As 700,000 residents already suffer from noise pollution as a result of Heathrow flights, we also hope any plans to expand Heathrow can soon be laid to rest. In the short term using existing capacity in a smarter way may be the most cost-effective solution.”

The committee’s report is the London Assembly’s response to a consultation on aviation capacity which was set up by the government last year and is being headed by Sir Howard Davies. It is expected to report with interim findings at the end of this year.