Example prices: Midland Mainline Sheffield-London

First Premier: Now �161. From 6 Jan �177 Standard Open: Now �95. From 6 Jan �99 Standard Saver: Now �48. From 6 Jan �48.30 Apex: Now �29. From 6 Jan �29

Midland Mainline's first class and standard open fares are up by 10% - well ahead of the UK's 1.8% inflation rate - while "leisure-based" services are increasing by between 2% and 4%.

First Great Western is freezing many fares, although its first and standard open fares will rise by between 3.5% and 4.4%.

GNER is similarly raising first and standard open fares by an average of 2.8%, but said some discounted fares may be reduced.

Virgin is freezing its fares, while ScotRail is freezing all fares except for single tickets, in what it says is an attempt to discourage people who dodge the return fare.

The increases were first announced last month, and will take effect at midnight on Saturday.

Passenger protests

Passenger groups said frequent delays and cancellations on the railways make above-inflation fare increases unjustifiable.

"Given the current performance of Midland Mainline, which even they admit is poor, it is difficult to see how passengers can be expected to pay substantial increases now for a promise of improved performance in the future," said a spokesman for the Midlands Rail Passengers' Council.

Business passengers on some long-distance routes and travellers who do not book ahead will be hit hardest by the rises.

The railway companies claim the fare increases are needed to fund urgently-needed investment programmes.

But in the south-east of England, commuter lines are being forced to lower some ticket prices because of continued poor services.

Many season ticket prices will be up to 7% cheaper, making some fares lower than they were a decade ago.

SWT strike row

The fare increases come into force as South West Trains, one of the UK's busiest rail companies, faces a second 48-hour stoppage due to strike action next week.

Members of the RMT union staged an initial 48-hour walkout on SWT lines on Thursday in protest over pay and conditions, leaving some 150,000 passengers stranded.

Transport Secretary Stephen Byers, still facing criticism for forcing track and signals operator Railtrack into administration in November, came under renewed pressure from the Conservatives to resign because he went on holiday during the SWT crisis.