Overcrowding and delays may be on the cards for Chester rail passengers, following the discovery of corrosion on a fleet of Arriva Trains Wales' diesel trains.

But the rail provider is hoping all the necessary maintenance work will completed by the summer.

Four Class 175 Coradia units operated by Arriva Trains Wales are already out of service at the company's Chester depot, and all its other 175s – which are used on most Holyhead-Cardiff and Llandudno-Manchester services – are in need or urgent repairs.

Arriva Trains Wales has no current plans to hire additional trains.

A company spokeswoman said: “We can confirm four of our 175 units are currently out of use for corrosion repairs, also our 150 fleet is undergoing corrosion repairs.

“We have not seen any significant impact on performance.

“However we’ve tried to use 158 stock instead of 150 stock where possible as 158s can attain 90mph vice a 175’s max speed of 100mph (and there are not very many 100mph stretches of track on our network.)

“We have obviously tried to allocate the replacement two-car fleet to the quietest services where possible but some affected peak time services have been busier than usual.

“We will not be sourcing any extra capacity due to the timescales involved and lack of availability and there are no plans to use loco stock on the weekends.

“We hope that all of the corrosion maintenance work will be completed by summer 2016.

“We regret any inconvenience that this has caused to our customers whilst we carry out this essential maintenance work.”

Charlie Hulme, who runs an online noticeboard on the North Wales coast railway, said the corrosion affects window frames, stump pillars and solebars.