Twelve UK train drivers have been banned from working after failing or refusing to take drug or alcohol tests in the past 18 months, The Independent can reveal.

The bans coincided with a spike in numbers of trains triggering safety alerts – although an industry body says the test failure figures are relatively low, and it believes a link is unlikely.

Figures show that since June last year, the rail watchdog has withdrawn four licences for drivers for failing drugs tests and two for failing alcohol tests.

Five were treated as failing both a drug and alcohol test; in fact they may have taken either alcohol or drugs, but the information sent to the regulator did not specify. One refused to take a test.

The 12 drivers were among 86 who had their licences suspended or withdrawn in that period for reasons including issues with competence training, failing a medical, medical or psychological reasons, passing signals at danger, resigning and retirement.

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And since April this year, five rail maintenance staff have failed random drug and alcohol tests, according to Network Rail figures.

A string of official figures on “spads” – signals passed at danger – all show rises since last year:

In July this year, 41 red lights were passed – more than one a day – making it the worst single month since October 2007

From April last year to April this year, the number of trains that passed through red signals – 304 – reached a 10-year high

In the 12 months to August this year, trains reaching the “conflict point”, the position along the track at which a collision could theoretically happen, reached a five-year high. In all, 10 passed red signals to get to that stage – higher than the five-year annual average of between four and five, and higher than the total for the financial year 2018-19, which was seven.

In 2019, there have been 25 instances where the train reached Network Rail’s “fouling point” – or conflict point. This was an increase from 18 last year.

The spike in red signals being passed prompted safety authorities to launch an investigation and to ask train companies and Network Rail to act to reduce the risk of crashes.

Twenty years ago, the Ladbroke Grove train crash killed 31 people and injured more than 250 people after a signal was passed at danger.

However, the Rail Safety and Standards Board, an industry body set up in response to the disaster, says that in the past 20 years, the industry has reduced spad risk by more than 90 per cent. It has been more than 12 years since the last train accident involving fatalities, and today Britain has “one of the safest railway networks in Europe”.

A spokesman said although the causes of the new spike in spads were still not known, he doubted it was linked to drink or drugs, saying the vast majority were caused by momentary lapses in concentration or a brief misunderstanding of details such as braking power or adhesion to the lines.

“The big picture is the overall risk reduction is very good but you only start to spot issues if you keep an eye on the data to catch any issues early,” he said.

Braking a tenth of a second too late, for instance, could make the difference in a few metres, and still be within safety limits.

Train driver alcohol limits are much stricter than for road driving – at 13mcg of alcohol per 100ml of breath, against 35mcg. Tests may be carried out at random, and are always done after a signal is passed at danger.

However, all rail companies and Network Rail have zero tolerance policies on drugs and alcohol.

The Office for Rail and Road, which provided the figures on licences suspended and withdrawn, started gathering the data only last June so could not make comparisons with previous periods.

Research was done this year into driver boredom – or mental “underload” – where tasks are repetitive – and techniques are being offered to help drivers stay alert.

The UK’s 20,867 train drivers must undergo medical examinations at least every three years.

Bruce Williamson, of Railfuture, an independent organisation campaigning for better passenger services, said it was right that everyone knew the latest figures on drivers who were banned.

“Any passenger would be rightly concerned if they thought their driver was over the limit, as on a bus or plane, but our safety record in the UK is excellent.

“The problem is that stopping is still to a large extent down to drivers observing signals rather than automated, and it’s poor that spads are still possible.”