Birmingham's reputation as a national business centre is being seriously damaged by Network Rail, officials said last night.

With passengers facing another day of disruption as engineering works on the West Coast Main Line continue today, fears were voiced that the delays are costing the region's economy millions of pound.

As a passenger watchdog questioned NR's credibility and the Rail Regulator hinted it could be facing a multi-million pound fine, Virgin Trains advised commuters to steer clear of its services today.

NR admitted it could not say when the work at Rugby - meant to have been completed by New Year's Eve - would be finished. According to some reports however, a source claimed work on the main line between Birmingham and London at Rugby was likely to carry on until Monday at the earliest.

Yesterday's problems coincided with Virgin's inflation-busting ticket price rises, with the annual cost of a season ticket between Birmingham New Street and London Euston increasing from £7,260 to £7,608.

Commuters returning to work after the New Year were hit by the chaos on the rail network, leading to a knock-on effect as people turned up late for work or not at all.

Jerry Blackett, chief executive of the Birmingham Chamber of Commerce, said: "The Birmingham economy is worth £20 billion a year to the UK economy - equating to £55 million a day - and we can't afford too many days like today that don't work properly.

"Our greatest asset is our central location, but situations like this only reinforce the negative stereotype that Birmingham is a difficult city to get in and out of.

"This main line is vital to those companies that are doing business in London and the delays today would have hit meetings and commuters.

"We can't afford to have people forced to stay away from their offices at home because of transport problems. They will have been raring to go after the Christmas break and this will have put a dent in their plans for a positive start to the New Year."

Paul Fullwood, secretary of the West Midlands Rail Passengers Committee, said passengers were getting "resigned" to disappointing service from the rail network.

He said: "We understand the background to this and we share some of Virgin's frustrations with Network Rail.

"Passengers are paying more and the rail industry must keep its side of the bargain. There are a lot of commuters coming in from Northampton who might have been expecting to start work today.

"And it's particularly disappointing on a day that the fare raises have come in. It will have disrupted people's lives in a lot of ways.

"Clearly Network Rail have thrown men and rail resources at this but it's calling into question their ability to manage the rail network, and it calls into question the future of what they are doing.

"And you worry about what will happen in the future if this has gone wrong like this."

The Office of Rail Regulations (ORR) said it had launched an "urgent" investigation into the over-runs.

In July last year, the company was fined £2.4 million after signalling work at Portsmouth overran in 2006, causing delays for more than nine months longer than anticipated.

ORR chairman Chris Bolt said Network Rail could be facing the same treatment again, adding: "It is extremely disappointing to have a repeat of that experience, on key parts of the network.

"As part of our investigation, we will review Network Rail's whole programme for completing the West Coast works in a way which meets the requirements of passenger and freight train operators and of funders."

A spokesman for NR apologised for the delay in finishing the engineering work, and said extra workers were being brought in to sort the problem as quickly as possible.

* Passengers' misery was further compounded yesterday by a fire at Birmingham International, closing the station for about 45 minutes. A small fire had broken out in a cafe at 10am.