The horror stories are many. The pensioner physically dragged, crying, off a crowded train by two "revenue protection" goons because she had forgotten her senior citizens railcard. The passengers stung for £20 because there was a queue at the ticket office and they had to hop on without paying or miss the train. The people bullied into paying unfair penalties by empty threats of prosecution and a criminal record. Today, however, the Standard tells you how you may never have to pay another railway penalty fare again.

Penalty fares - 20 years old this month - began life under British Rail as a reasonable deterrent to fare-dodging. But for some of the privatised rail companies, these £20 fines for not having a ticket have become nice little earners in their own right. One operator made £32 million from them last year alone. Another, Stagecoach's South West Trains, sparked outrage when it started judging its guards' job performance by the number of penalty fare warnings they issued.

Many passengers complain of a "take-no-prisoners" attitude, even where travellers have good reasons for not buying a ticket and every intention of paying. They say they are being penalised for train companies' failure to provide adequate station ticket offices, with staff and opening hours cut even as passenger numbers have risen.

But what most people do not know - and what the train companies are understandably reluctant for us to find out - is that more than a few demands for penalty fares are arguably illegal. The railways' new, hard-line approach is essentially a gigantic bluff, relying on our ignorance of our rights and our unwillingness to make a fuss when collared.

Because you do, in fact, have quite extensive rights not to be charged penalty fares, many of them set out in law. Rights designed, in the words of the Government, to "make sure that the interests of honest passengers are protected".

The chances are that if you have a reasonable excuse not to pay a penalty fare, you do not have to pay it - whatever a train company's staff may claim. If you are prepared to quote your rights and call their bluff, you will usually prevail.

Provided always that you do pay the normal single fare, the chances are that any threats made against you, particularly of criminal prosecution, are hollow.

Richard Colbey, a barrister at Lamb Chambers, told the Standard: "The policy is legally dubious. Penalty fares are not enforceable unless a court orders it - and a court would be unlikely to do so with someone prepared to make a fuss. There has been no reported case of a train company suing in this way - the last thing the rail industry would want is a pronouncement by a judge on its levying of penalty fares."

Another leading rail industry lawyer told the Standard that he had himself been threatened with prosecution for not paying a penalty fare. "I wrote them a very polite letter explaining why I had not got a ticket," he said. "I told them to have a go if they felt like it and heard nothing more."

I, too, have several times successfully refused to pay penalty fares demanded of me in circumstances which were unreasonable. So here is the Standard's summary of your rights - and our advice on avoiding unfair penalty fares.

OUR 10 RULES FOR BEATING THE TICKET INSPECTOR

This advice is for National Rail services only. TfL has different rules with fewer safeguards. No legal liability is accepted.

1 Make a reasonable effort to buy a ticket before you get on.

It will weaken your case if you start from a station where there is a functioning ticket office or machine but make no attempt to use them. This does not, however, mean that you have to wait in a long queue and miss your train. See Rule Eight for the Government's guidance on what constitutes a reasonable waiting time.

2 If asked for a penalty fare, check that you actually have to pay one.

There are several non-penalty fare locations in London and the South- East - most importantly, Stansted airport. If your journey started at one of these locations, you cannot be charged a penalty fare. This probably applies even if you changed trains on to a penalty-fare service en route (see other box for full details).

There are other lines on which one operator has penalty fares and another does not (see box). If, for instance, you are asked for a penalty fare at the excess fares office at Euston and you have arrived on a train run by Virgin, not London Midland, you do not have to pay the penalty.

If you forget your season ticket, you do not have to pay a penalty fare. You may be issued with a "nil fare" penalty notice and asked to send in a photocopy of your season, or asked to buy a normal single ticket (which you can then get refunded at a ticket office on production of your season). You can only do this twice a year.

If you have a ticket between two places with multiple rail routes (eg London-Southend) but it is not valid for the route you are using, you cannot be charged a penalty fare - only the difference in price between the routes.

If you have a ticket for the right journey but it is not valid on the particular train you are using, this is a grey area. The Department for Transport's "Penalty Fares Policy" (clause 4.29) says you should not be charged a penalty fare, just the difference in price. But the National Rail conditions of carriage say holders of "some types of discounted tickets" can be charged a penalty. It is definitely worth arguing the point.

3 Check that the person asking for a penalty fare is an "authorised collector".

Under the Penalty Fares Rules 2002, sections 5 (2) and (3), only an "authorised collector ...individually authorised by or on behalf of the operator of that train" is allowed to collect penalty fares. Not all train guards and excess ticket office staff are authorised collectors. You have the right to ask them to produce the special identification document which proves that they are. (This also helps to return a measure of the "embarrassment factor", which some collectors use to get travellers to pay up.)

Check also whether the person asking you for a penalty has been authorised by the operator whose train you travelled on. At stations served by more than one train company, even where they both have penalty fares schemes, it may be that the people on the ticket barrier are authorised by one operator but not by the operator you used.

4 Even if they pass these tests, politely refuse to pay the penalty and simply pay the full single fare.

On the train or at the station, you have the absolute right to make only "a minimum payment that is equal to the full single fare which [you] would have had to pay for [your] journey if penalty fares had not applied." This is section 8 (2) of the Penalty Fares Rules 2002 - quote it if anyone tries to tell you different. (The full single fare means the fare without any railcard discounts, cheap offers etc.) Ignore any threats that may be made at this point if you refuse to pay the full sum - these are phoney and have no legal basis.

5 Never pay the penalty in the belief that you can recover it on appeal.

You are allowed to appeal against a penalty fare to one of two supposedly "independent" bodies. Most operators use the Independent Penalty Fares Appeals Service (IPFAS), others the Independent Appeals Service (IAS). But IPFAS is in fact owned by Southeastern Trains, is based at Southeastern's head office and all its staff are Southeastern employees. IAS was also until recently based in railway offices and its company secretary is a director of the company which runs the railways' ticketing system. In short, the appeal process is not independent of the rail operators, is not operated in your interests and is most unlikely to recover your money.

6 Give your correct name, address and journey details.

Once you have paid the single fare, the collector will then ask for your name and address so that they can send a demand for the rest to be paid within 21 days. They can check names and addresses while you wait with the electoral roll database. The only criminal offence in the whole penalty fares legislation is refusing to give a name and address, or giving a false one. So give the right details.

7 Once you have paid the minimum, they will hand you a form.

Check this carefully. It must show the authorised collector's name and identity, your correct details, the details of the journey you have taken and how much you have paid. Collectors are often careless. If any of these details are omitted or are wrong, and you can prove it, it is game over.

8 When the letter demanding the rest arrives, write back politely, again refusing to pay, and explaining why you were unable to buy a ticket before travelling.

This is where the most useful part of the Penalty Fares Rules comes in - Rule 7 (4), which states that a penalty fare must not be charged "if ... there were no facilities available for selling the appropriate ticket or other authority for the journey the person wanted to make".

The Rules themselves do not define what "no facilities available" means. But in separate guidance on penalty fares ("Penalty Fares Policy") issued by the Department for Transport, it is made quite clear, in clauses 4.2 and 4.11, that passengers must be given "sufficent opportunity" to buy a ticket and that regular queues over three minutes (off-peak) and five minutes (peak) breach the definition of what is "sufficient".

It is not clear whether this definition has any legal force - but if you quote it in your letter back to the train company, you are unlikely to be bothered again.

The Penalty Fares Policy also tells companies to "use discretion" towards the elderly, pregnant women, people who have enough money to buy a ticket "but not in the form needed to use the [ticket] machine" and "all passengers when the train service is severely disrupted". Once again, if you can truthfully quote any of these, you are unlikely to be bothered.

9 Remember: penalty fares are a civil, not a criminal-matter.

Train companies often scare people into paying up by threatening prosecution and a criminal record. However, the legislation establishing penalty fares, the Railways Act 1993, section 130, states that apart from failing to give your right name and address, "nothing in this section creates, or authorises the creation of any [criminal] offence". The Penalty Fares Regulations 1994 state that "the recovery of a penalty fare is a civil debt". So even if after reading your letter the company still decides it wants the money, it has to sue you - probably not worthwhile for such a small sum.

Railway companies sometimes threaten people with the main criminal law against fare-dodgers, the Regulation of Railways Act1889. But this says there has to be "intent to avoid payment". You could argue that you haven't intended to avoid payment because you have, in fact, paid the full single fare.

10 But don't abuse the system.

The safeguards provided in the law and the regulations are intended for people who want to pay the proper fare but occasionally fall foul of inadequate facilities. If you constantly board trains without buying a ticket, or if you lie to train company staff, this could be construed as intent to avoid payment and the chances of criminal prosecution will rise.