The wreckage blocked adjacent lines and was struck within seconds by a "double-headed" express train travelling north at 60 mph (100 km/h).

[7] At 8:19 a.m, just as the guard was walking back to his brake van after checking doors on the last two carriages, the Perth express crashed into the rear of the local at a speed of 50–60 miles per hour (80–100 km/h).

A few seconds after the first collision, the northbound express to Liverpool Lime Street passed through the station on this line in the opposite direction at approximately 60 miles per hour (100 km/h).

[5] The leading seven coaches, plus a kitchen car from the Liverpool train, were carried forward by momentum, overriding the existing wreckage and piling up above and around it.

[11] Sixteen vehicles, including thirteen coaches, two bogie vans and a kitchen car were destroyed or severely damaged in the collisions.

[5] The Ministry of Transport report on the collision was written by Lt Col GRS Wilson, a senior member of the Railway Inspectorate, and published in June 1953.

Having thus missed the Distant he may have continued forward past Headstone Lane station (which was not on his own side), underestimating the distance he had run from Hatch End and still expecting to see the colour light and not the Harrow semaphore stop signals which were at a considerably higher elevation.

Railway safety depended on obedience to signals, and the report saw no need for more restrictive ways of working to accommodate driver error;...the Rules and Regulations for train working in fog have proved adequate in practice with the aid of the professional skill and care which is displayed by engine drivers throughout the country on the vast majority of occasions.

The way to guard against the exceptional case of human failure of the kind which occurred at Harrow does not lie in making the regulations more restrictive, with consequent adverse effect on traffic movement, but in reinforcing the vigilance of drivers by apparatus which provides a positive link between the wayside signals and the footplate.

[21] The report considered a system warning drivers that they had passed a signal at caution or danger would have prevented ten per cent of the accidents (and 28% of the consequent deaths) in the previous forty-one years, thereby potentially saving 399 lives, including the 112 at Harrow.

By the time the report had been published, a five-year plan had been agreed to install the Automatic Warning System on 1,332 miles (2,144 km) of line.

All, however, are agreed that enginemen should be given their share of technical aids to safe working, and I consider that at this late stage there should be no reservations on the rate of progress once the apparatus has been approved.

[23]The accident accelerated the introduction of British Railways' Automatic Warning System (AWS),[24] which had received scepticism by some industry expenditure-prioritising experts who theorised more lives would be saved by installing more track circuits and colour light signals.

[28] A mural along the bordering road, featuring scenes from Wealdstone's history, was painted by children from local schools and dedicated in memory of the victims.