The competition watchdog has introduced a price cap on certain rail routes in the North West and Scotland.
It comes after fears that the new franchise could lead to an increase in fairs, the agreement was secured as part of the joint venture between First Group and Trenitalia to operate the West Coast Mainline.
Competition and Markets Authority said the fares cap will be introduced on 21 routes between Preston and Scotland being run by the joint venture, which has been named Avanti.
The CMA originally had concerns that passengers could be "facing higher fares and less availability of cheaper tickets" due to limited competition under the new franchise deal.
It said its phase one investigation into the contract found competition issues on 21 routes - four between Oxenholme and Carlisle and 17 between Preston and Glasgow and Edinburgh.
On the 17 routes between the North West and Scotland, passengers will only be able to travel on the Avanti service or TransPennine Express, which is solely run by FirstGroup.
On the other four routes, passengers can still only choose from three operators, the CMA said.
However, the CMA said it has now accepted the franchise deal after First Group and Trenitalia agreed to price caps to address its concerns.
It said the rail service providers committed to "caps on unregulated fares and maintaining the same availability of cheaper advance tickets for all 21 routes" on both the West Coast Rail and TransPennine Express services.