Plans for a rail link between the Great Western mainline and Heathrow Airport will be delayed by up to two years.
A planning application for the long-anticipated scheme, which would allow people living to the west of Heathrow to travel direct to the airport, had been expected this year.
But Network Rail said the proposal had been delayed by the impact of Covid-19.
Reading Borough Council's lead for transport Tony Page described the delay as "deplorable".
According to the £900m proposal trains would run every 15 minutes from Reading to Heathrow, with a journey of less than half an hour.
Currently rail passengers from the Thames Valley, Wales and the West have to travel via London.
They said in a statement: "The Department has been clear that whilst it fully supports the development of a Western Rail Link to Heathrow, this is subject to a satisfactory business case and the agreement of acceptable terms with the Heathrow aviation industry."
The DCO is expected to be submitted next winter.
'Could be held for much longer'
By BBC South Today transport correspondent Paul Clifton
Trains from Reading to Heathrow would transform travel to the airport.
Millions of passengers from across the South, West, Wales and the Midlands would no longer need to travel through London.
The plans have been in place for years. The platform space already sits beneath Terminal Five, as an empty concrete box. Reading station, rebuilt in 2014, was designed with the Heathrow service in mind.
The Government had expected Heathrow and its airlines to put significant money in the pot, because they would get substantial benefit. But the business case has evaporated during the pandemic.
Heathrow no longer has spare cash to invest in a rail link. It has officially been put back for up to two years. But there must be a very real risk of this nationally important infrastructure project being on hold for much, much longer than that.
Speaking to the BBC, Mr Page said: "I think it's quite deplorable because for many years Heathrow has good needed rail links and improved public transport just for the original airport.
"Reading Station was planned on the basis of a platform for a Western rail link to Heathrow as well as Crossrail."