A weak bridge which has blocked the railway between Didcot Parkway and Oxford is likely to remain closed for at least two or three weeks, GWR has warned, which means there can be no through services between Didcot and Oxford over the Easter weekend.

Trains are continuing to run mainly as usual on the North Cotswolds Line from Hereford and Worcester to Oxford, but CrossCountry passengers using the Bournemouth to Birmingham and Manchester route must change to a replacement bus between Didcot Parkway and Oxford.

Network Rail engineers are investigating the problem affecting Nuneham Viaduct, which carries the Cherwell Valley Line across the Thames between Culham and Radley.

The Rail Freight Group said the line usually carries 40 freight trains a day. Diverting them is not easy, because not all alternative routes have adequate clearances for the largest containers.

Network Rail had been monitoring the viaduct for some time because movement had been detected, and had been trying to stabilise it. The very wet March this year may be a factor.

GWR said: ‘Unfortunately, the movement in the structure has significantly worsened in recent weeks and has now reached a point where it is not safe.’

Replacement buses are running between Didcot Parkway and Oxford, while GWR also advised its passengers from the Oxford area to drive to Didcot and use the multi-storey car park if they could. Chiltern Railways has urged passengers not to use its services in the area over Easter unless they must, because its trains between Oxford and London Marylebone are very busy.

GWR managing director Mark Hopwood said: ‘This is a significant route and we are exploring all avenues to be able to bolster services between Oxford and London.

‘To help keep customers on the move we’ve mobilised colleagues to assist at key locations. We’re also looking at what we can do in the longer term, including the possibility of running GWR trains on alternative routes between Oxford and London.’

Network Rail’s interim Western route director David Davidson added: ‘We are sorry for the disruption this has caused for passengers and advise them to continue to check before they travel.

‘Safety is our top priority and our engineers are now working round the clock to identify what can be done to make this viaduct safe for passenger and freight trains to run again.

‘We are disappointed that the work we’ve done so far hasn’t been successful, and our efforts haven’t been helped by the wettest March in over 30 years. We will continue to provide updates as we work to reopen the line as quickly and as safely as possible.’