New measures to combat an estimated £10m in annual lost revenue due to fare evasion and fraud will be introduced in South Wales this month.

Penalty fares will start on the South Wales Mainline from Monday, March 4.

Initially planned is a three-week period of guidance to customers, during which anyone travelling without a valid ticket for their journey will be advised on potential consequences by authorised Revenue Protection Officers.

Then, from March 25, passengers found to be travelling without a valid ticket will be slapped with a penalty fare of £20 or twice the full fare, dependent on which is higher.

The new enforcement will apply to routes that span Severn Tunnel Junction in east Wales and Carmarthen in west Wales on Transport for Wales (TfW) services.

Chief commercial officer at TfW, Alexia Course, said: "The vast majority of customers pay the correct fares and this revenue is vital for us as we continue to transform the Wales and Borders network with £800m of brand-new trains and the delivery of the South Wales Metro."

She said the minority who evade payment not only burden their fellow passengers but also cause significant loss to TfW each year.

Ms Course emphasised that all revenue is used for running services and future enhancements, as TfW is a non-profit organisation.

By reducing fare evasion and fraud, they can also lower the subsidy required from the Welsh Government, which is funded by taxpayer money.

Plans are underway to expand this to the rest of the network over the coming months.

Penalty Fares will be administered by authorised Revenue Protection Officers tasked with checking tickets and issuing Penalty Fare Notices to those found without a valid ticket.

They can also issue Unpaid Fare Notices (UFNs) to passengers who cannot pay the Penalty Fare immediately or who have committed a more serious offence.