Britain is in the grip of a pickpocketing epidemic as Eastern European gangs descend on London ahead of the Olympic Games.

A surge in sneak street thefts means more than 1,700 people fall victim every day – an increase of nearly a fifth in only two years, according to official crime figures released yesterday.

At the same time, police warned that professional gangs from Romania, Lithuania and even South America who operate in capitals across Europe are heading to Britain, intent on cashing in on unwitting tourists at London 2012.

A BBC investigation exposed the tactics used by Romanian thieves, who were previously operating in Barcelona, to dupe their victims.

The criminals boasted of their ‘one-second’ theft techniques which leave targets unaware that anything has happened until it is too late. They can make £4,000 a week taking wallets, smartphones and laptop bags. The goods are then shipped back to Romania and sold on the black market.

Scotland Yard has made more than 80 arrests already and warned thieves the capital will be a ‘hostile environment’ in the coming weeks.

The Met has even drafted in a team of Romanian police officers to deal with the problem and patrol in the West End of London and Westminster during the Games. They will not have arrest powers.

Mayor of London Boris Johnson said: ‘These Romanian officers will prove to be a huge asset in cracking down on certain criminal networks who are targeting tourists in central London.’

Official statistics released yesterday showed pickpocketing thefts rose 17 per cent in the past two years.

In 2011/12, a total of 625,000 people fell victim, the Crime Survey of England and Wales showed.

That is an increase of more than 102,000 since 2009/10. The vast majority of the total are classified as ‘stealth thefts’, but in 83,000 cases the victims’ possessions were ‘snatched’.

The BBC report showed the first member of a pickpocket gang approaching their victim with a request for directions.

Another member of the gang then plays drunk to get close to the target, while taking their wallet or mobile phone. The stolen goods are handed to a third member and quickly spirited away.

The thieves told the BBC reporter they were examining online maps of London to help plan escape routes.

Detective Inspector Mark Teodorini, the head of Scotland Yard’s Olympics crime team, called for public vigilance. Officers have conducted a series of raids in recent weeks on properties where suspected thieves were living.

He said: ‘We know where people are. We know the addresses they are using, we know the vehicles they are using, and we will come through their door very robustly – and if we find anything on them, we will arrest them.’

He added: ‘We won’t always get them in the act but we are trying to disrupt their activity.

‘It is going to be a hostile environment for pickpockets. My advice to them is “don’t bother”.’

Javed Khan, chief executive of Victim Support, said: ‘The rise in pickpocketing, thefts of wallets and unattended bags is worrying and can be the cause of upset for many victims.

‘So we cannot afford to be complacent in the fight against crime.’

In April, a family of Romanian pickpockets who built expensive homes in their home country with the proceeds of thefts from commuters were jailed.

The Rostas family targeted up to 1,000 train passengers who slept on late trains leaving London. Five members of the family were jailed for a total of ten years.