When railway privatisation started in Britain, potential operators were invited to bid to run bundles of train services in specific geographic areas. They had to operate a specified minimum timetable, but were free to run more trains if they wished. Indeed, on some inter-city lines, the minimum specified was half of the then current timetable: it was thought that new commercially minded private sector operators would of course fill the gaps to increase their revenue.

The former British Railways fleet of passenger rolling stock was sold to three rolling stock leasing companies - ROSCOs - and potential operators were free to lease what they wanted, or to buy their own.

This ideal needed dilution in practice because some stock is route specific and some routes are stock-specific. For example, the dual-voltage class 319 electric multiple units were the only trains capable of working the Thameslink route between Bedford and Brighton. Because they were also highly efficient for working either on AC services north of the Thames or DC services south, they were likely to be wanted by other operators too. Someone had to moderate things so that Thameslink got its trains.

Over time, things have changed - evolved is probably too strong a word!

The timetable specification is now significantly more prescriptive - not just the number and frequency of trains, but also the number of vehicles the operator is allowed to lease.

Franchises specify train frequencies over the life of the franchise, and also flavour-of-the-month issues like requiring station entrances and exits to be gated - to have automatic barriers. This was thought likely to reduce anti-social behaviour like vandalism and graffiti. The fact that the operator might wish to deter such things - and at the same time control revenue and increase passenger satisfaction - by putting on more staff at stations instead seems not to have affected any decision making processes. Nor does the fact that ticket barriers are rarely effective - stand at any station where there are unmanned barriers around 10 at night and either the barriers will be locked open, or passengers will be vaulting over them or sliding through the luggage gate with the ease of long practice.

As ever, a mix of civil servants and elected politicians playing trains has led to a less-than-satisfactory result in places.

The exact status of franchise requirements is unclear - to me, at least, and any light readers can shed would be appreciated.

Supposing a train operator fails to run the right number and length of trains? Some of this - train running and punctuality - is monitored through things like the Public Performance Measure, the PPM. But what about other infractions? Things like failure to install ticket barriers, for example? It is certainly possible that, at some historic stations, local planning authorities might object on conservation grounds to such things - so one authority would be insisting on installation when another was refusing permission. I've lost touch with the York story, but it was proceeding along those lines.

At one time, the former Strategic Rail Authority (SRA) named and shamed defaulting operators. It reported, in its best-selling annual report, the most minute failures to comply with franchise conditions - displaying ticket office opening times in the wrong size print and the like.

One sanction, of course, is the threat of non-renewal of franchises, or not granting franchises to awkward operators. When the SRA proposed withdrawal of Gatwick Express some years ago, they were taken aback by the very robust response they got from BAA - a strongly worded report entitled, "The Murder of the Gatwick Express" (in whose preparation I participated). The SRA were not accustomed to train operators opposing their suggestions: BAA could get away with it because they were not dependent on the SRA for the grant of future franchises.

The issue gets even more interesting with the advent of Route Utilisation Strategies, produced by the infrastructure owner Network Rail. These too can be prescriptive - or restrictive - and again their precise force is unknown.

For example, there is a franchise requirement to run four non-stop trains an hour between London Victoria and Gatwick Airport: the recently-published Sussex Route Utilisation Strategy proposes stopping between 2 and 4 of the high peak ones at Clapham Junction, despite numerous representations over the years from the aviation industry that a non-stop service is what is wanted.

There is a franchise requirement for two trains an hour between Reading and Gatwick - but Network Rail consistently argue that there are not enough paths to run these between Gatwick and Redhill.

I understand that, in such cases, it is up to Network Rail to formally tell the government that it cannot meet train operator requirements with the existing infrastructure and needs the money to fund some more: no-one is holding their breath waiting for results!

There is a strong suspicion that railway privatisation in Britain has been characterised by excess haste and a tendency to make up policy on the hoof. Conflicting and unnecessary requirements of the Department for Transport and Network Rail on train frequencies and other commercial details do not help.