Facing the possibility of cancellation, BR management decided to put the prototypes into service, with the first runs along the London–Glasgow route taking place in December 1981.

By this time the competing High Speed Train, powered by a conventional diesel engine and lacking the APT's tilt and performance, had gone through development and testing at a rapid rate and was now forming the backbone of BR's passenger service.

The extensive work on electrification carried out alongside the APT was effectively utilized in later non-tilting designs, including the British Rail Class 91.

[2] Jones was convinced that hunting oscillation was an effect similar to the problem of aeroelastic flutter encountered in aerodynamics, and decided to hire someone from the aeronautics field to investigate it.

[4] This work was then extended to the unique two-axle bogieless car designs used on the BR freight network, where the problem was further modified by the dynamics of the entire vehicle.

The key realization was that the suspension had to be both vertical, as it had been in the past when based on leaf springs, but also horizontally to avoid small displacements triggering oscillation.

[7] During this period, BR's Passenger Business division produced a report suggesting rail could compete with road and air, but only if the trains ran faster.

[4] This presented a problem for any sort of high-speed operation on the route because the existing line contained many turns and curves, and rounding these at high speed would cause lateral forces that would make walking difficult, and throw items off tables onto the floor.

[8] Given the curve radii typically encountered on the WCML, this meant that even with the maximum permissible amount of cant applied, speeds couldn't be increased much above the 100 mph (161 km/h) range without once again experiencing excessive lateral forces.

When the train rounded a bend, the centrifugal forces caused the car body to swing out like a pendulum, reaching the proper tilt angle naturally.

A major advantage for BR use was that the center of rotation could be through the middle of the car, instead of the top, meaning the total movement would fit within the smaller British loading gauge.

Accordingly, later that same November, Newman and Wickens drew up plans for a complete experimental train with the design goal to be not only to study the tilt system, but do so on actual lines.

In spite of being repeatedly put off, Jones persisted, especially with Government Chief Scientist, Solly Zuckerman,[4] to arrange a stable funding system for the entire topic of railway research.

Offsetting this effect required the train to meet stringent weight limits, and eliminated the possibility of using conventional diesel engines, which were simply too heavy.

[4] When the funding was secured a number of design notes were still not finalised, so the timeline was stretched into July 1971 to provide extra time for the project definition stage.

Other changes included the removal of the ceramic recuperators from the turbines for reliability reasons, although this dramatically increased fuel use, and the addition of a small seating area to the passenger car for VIP use.

The company agreed to continue supporting the project anyway, including the release of a more powerful 350 horsepower (260 kW) version, but made it clear a production design would have to find another solution.

[4] With the decision to move primarily to electrification made in November 1972, Jones began building a larger management team to carry the design forward to service.

[19] As part of the same review, the team noticed that a slight reduction in maximum speed would greatly simplify a number of design points, and eliminated the need for the hydrokinetic brakes.

They proposed building a much simpler design, powered by conventional diesels and lacking tilt, but capable of speeds of up to 125 mph (201 km/h) and able to run anywhere on the BR network.

Each driving van trailer i.e. the leading and trailing vehicles, was equipped with a diesel-alternator generator capable of supplying the minimum requirement of auxiliary power.

[4] While the commissioning team continued to report, and solve, problems in the APT design, BR management was under increasing pressure from the press.

On 7 December 1981 the press was invited aboard APT for its first official run from Glasgow to London, during which it set a schedule record at 4 hours 15 minutes.

[25] On its return trip from London the next day, one of the coaches became stuck in a rotated position when the tilt system failed, and this was heavily reported in the press.

[25] In 1981, BR hired the consulting firm Ford & Dain Partners to produce a report on the APT project and make any suggestions to improve it.

The work that suggested the amount of tilt needed to reduce the lateral forces to acceptable levels was eventually traced to a short series of studies carried out by a steam train on a branch line in northern Wales in 1949.

Writers generally agree that the technical aspects of the design were largely solved by the time of their second service introduction, and put most of the blame for the delays on the shifting management structures and infighting within BR between APT and HST.

There have also been concerns that carrying out development within BR was a major problem of its own, because this meant their industrial partners had no buy-in and their years of practical experience were being ignored.

[17] This number has been compared to the roughly £100 million spent by British Leyland to develop the Austin Mini Metro, a project that was technically trivial in comparison to APT.

The Mark 4 coach design that was introduced as part of the new IC225 sets for the East Coast Main Line electrification allowed the retrofitting of the tilt mechanism, although this was never implemented.