How many times have you found yourself unpacking your toiletries at airport security, proving every bottle is under 100ml – only to sheepishly discover the oversized shampoo you’d forgotten?For almost 20 years, air passengers have followed these rules.It turns out the hassle may all have been for nothing.A security expert has claimed the long-standing airport liquid restrictions are little more than ‘security theatre’.The 100 ml limit is still enforced at many airports around the world, although an increasing number are abandoning the rule as they introduce new scanning technology.But Bruce Schneier, a security technologist and fellow at Harvard University, says the restrictions are ‘absurd’. The limit on taking liquids over 100ml on board was just for show, it emerges’It’s 100 per cent security theatre,’ Mr Schneier told The Telegraph’s The Travel Expert podcast. ‘They’re not doing it based on security, they are doing it based on a compromise, which would make no sense if it was a security problem. ‘If I walk through airport security with a gun and they find it… they ruin my day. If I walk through security with a bottle of liquid and they find it, they throw it in the trash and let me through.’Because there’s no penalty for failure, there’s no reason not to try multiple times. ‘Here’s something so dangerous that you can’t take it on an aeroplane, yet so safe that [security officers] will throw it in a bin next to them.’So, why were the rules imposed in the first place?In the UK, liquid limits were put in place in August 2006, after a group of Islamists tried to smuggle liquid explosives disguised as soft drinks in their cabin luggage.Police uncovered the plot, preventing disaster – leading to a temporary ban on passengers carrying liquids through airport security.This was reduced in November of that year to the 100ml limit on board. It comes as many airports have begun to lift the restriction on taking liquids on board flightsHowever, airports across the country are now in the process of abandoning the rule.In January this year, Heathrow became the world’s largest airport to fully scrap the 100ml liquid limit.Heathrow Airport said it completed the £1 billion rollout of new scanners, which means passengers can keep liquids and large electronic devices in their hand luggage when going through security. Among other UK airports that have completed the rollout of the new scanners are Birmingham, Bristol, Gatwick and Edinburgh.