SOUTH West Trains is threatening its guards with disciplinary action - including possible dismissal - if they do not penalise passengers unable to buy a ticket before boarding with maximum fares.

A secret memo revealed the Hampshire company has instructed its guards to charge the most expensive peak fare, with no railcard discount, to anyone who gets on a train without a ticket.

It means passengers will usually pay more than double the normal price.

The leaked memo, headed "commercially sensitive, please do not circulate", instructs guards to treat passengers as fare-dodgers, even if they ask to buy a ticket.

It tells guards they will be accountable for accepting excuses, even if passengers say they have queued for 15 minutes and could have missed their train.

The memo also says children must be penalised, even at weekends and on bank holidays, when cheaper fares are available.

Guards must also tell passengers that they could be liable for an additional £20 on-the-spot fine or penalty fare, and could be prosecuted for fare evasion.

"From now, your commercial duties will be measured in three main areas: the amount of revenue that you collect; the type of tickets that you sell; and the number of penalty fare warnings issued," the memo says.

The revelations are the latest example of the lengths to which South West Trains is going to pay back a £1.2 billion premium over ten years demanded by the Government for its rail franchise.

And it comes just a month after South West Trains came under fire for a new round of fare hikes, which saw some off-peak fares go up by 20 per cent.

Passenger groups have accused the company of profiting from its failure to provide enough ticket facilities. South West Trains says it will install another 194 by September next year.

The Department for Transport said it was investigating queuing times at South West Trains' stations and would take action if the company was breaching regulations.

A recent survey by national rail watchdog Passenger Focus found almost two-thirds of South West Trains rail passengers said they were not getting value for money.

It showed that 41 per cent of the operator's passengers believed ticket prices were not justified.

However, overall customer satisfaction was above average.

A South West Trains spokesman said: "South West Trains is simply enforcing the existing policy that you must have a valid ticket before boarding.

"However if a passenger has a legitimate reason for not being able to buy a ticket, we will tell staff to use their discretion."

In similar circumstances discounts affairs would also still be available, he added.