COMMUTERS and passengers face “inevitable disruption” as work is carried out to electrify the main railway lines through Oxfordshire during the next seven years, Transport Secretary Lord Adonis said tonight.

He arrived at Oxford railway station during the rush hour to announce the line between Oxford and Didcot Parkway would benefit from the £1.1bn investment to electrify the Great Western main line between London Bristol, Cardiff and Swansea.

The line to Oxford is due to be electrified by December 2016, making services quicker and more environmentally friendly. Carriages will cause less damage to the tracks, leading to fewer line closures for engineering repairs.

Most commuter services between Oxford, Didcot, Reading and London will be operated by a fleet of modernised 100mph electric trains currently in use on Thameslink services across London. They are due to be replaced by new trains from 2012 and will undergo a major overhaul before moving to the Thames Valley, including the fitting of air conditioning.

Most of the work to electrify the route over the next seven years will be carried out at night and not peak times, Lord Adonis said.

He added: “This will serve to minimise the disruption to passengers. Network Rail will ensure that disruption is kept at a minimum.

“Of course there will be some significant work required at bridges and tunnels and inevitably there will be some disruption.

“But I believe passengers will regard the minimal disruption as worthwhile in the long term.”

Work preparing the tracks is expected to begin immediately and workmen will be spotted on the lines installing electrical equipment within the next two years.

Hybrid trains, able to use both electric and diesel power, will be introduced for longer-distance services, so passengers can continue beyond Oxford on journeys along the non-electrified Cotswold Line without changing trains.

Lord Adonis said there were currently no plans for the Chiltern or Cotswold lines to be electrified.

There will be no cuts in other areas of transport spending and fares will not be increased, he added.

Lord Adonis said: “It's a massive project. Oxford is a critical station on the network and it's very good news we will be giving passengers and commuters a more reliable train service that reduces costs and which are greener than the diesel trains.”

When the work is finished it will cut typical fast train journey times between Oxford and London Paddington from 56 minutes to 50 minutes.

Zahra Akkerhuys, of Grandpont, a spokesman for passenger group Ox Rail Action, said: “It’s a real step forward, but we're concerned about the general disruption that will take place in the short term or medium term.

“We have a sense of cautious optimism. We have seen an improvement in First Great Western’s services over the past year, but the service is far from perfect so anything that will improve it is welcome.

“Given Network Rail’s track record, we will need some reassurance that there’s not going to be chaos for years to come with this electrification.”

Yesterday’s announcement came five days after Network Rail began running replacement buses as it started six weeks of engineering work on the Cotswold Line between Oxford and Worcester in preparation for the laying of a second track along much of the route next year.