Building the London to Birmingham HS2 high-speed rail line will benefit towns and cities across southern England, according to a report.
A number of areas will have faster and more frequent services thanks to the new capacity that HS2 will free up, said Greengauge 21, a group set up to develop the case for high-speed lines.
Places which will get improved services include Lichfield, Tamworth, Nuneaton, Rugby, Northampton, Milton Keynes and Watford, said Greengauge 21 director Jim Steer.
Due to eventually run north of Birmingham, HS2 is a key part of the Government's transport strategy but is bitterly opposed by some groups as it passes through beauty spots and is not seen as offering value for money.
Mr Steer said: "Services which simply cannot be fitted on today's network will become viable once HS2 is built. Non-stopping inter-city services from the North of England and the Midlands to London will transfer across to HS2, making space on the West Coast Main Line for more freight on rail and more local services."
He added that rail services to a number of destinations would be "faster, more frequent and with much better connections, with peak-period travel restrictions ending".
Mr Steer went on: "It also becomes possible to operate new connecting and cross-country services that would need to travel short distances on the West Coast Main Line. So, East West Rail - the project long sought-after between Oxford and Milton Keynes - becomes possible.
"The case for the Croxley Link - near Watford - will be much improved because of the transformed service at Watford Junction."
Mr Steer said HS2 could also allow through-services from London to Wrexham and Shrewsbury again, while West Midlands services could be expanded.
Transport Secretary Philip Hammond said: "This is a welcome contribution to the debate on high-speed rail (HSR). We believe one of the key strengths of our HSR proposal is the benefits it could have for passengers on the existing rail network.
"We are already investing in more carriages to ease overcrowding for commuters, but a new high-speed line could offer them a transformational increase in capacity on existing lines."