By Costas Pitas

LONDON (Reuters) - The world's oldest underground rail network takes a big step forward this weekend when the "tube" starts all-night Friday and Saturday services after years of obstruction and delay.

In a move bound to please revelers, shift-workers and insomniacs, two lines will run trains through to 0530 in the morning, with others due to follow.

Traveler's in the capital have long been promised an overnight or later service but proposals had been postponed due to opposition from unions seeking better pay and conditions in return for working antisocial hours.

Now that agreement has eventually been reached, trains will run between north and south London and from east to west, before being rolled out on three further lines including to Heathrow Airport.

"It will support thousands of workers who have to travel to or from work at night, it will provide huge economic benefits to our vital night-time economy and it will help Londoner's get home quickly and safely after a night out," said Mayor of London Sadiq Khan.

The scheme is set to boost the capital's economy by 77 million pounds ($100 million) a year, according to the mayor, and could help support London's nightclubs and bars.

It will also go some way to catching up with train services in other major centers: the New York subway already runs throughout the night and the Paris metro operates late on weekends.

Once the full service is in place, 100 police officers will ride the network. Britain is on its second-highest level of security alert, "severe", meaning an attack is considered highly likely, though not imminent.

The first underground railway service ran between Paddington and Farringdon Street in central London on January 10 1863 and now the "tube," known the world over for its red roundel symbol, stretches well into London's suburbs and beyond.

Famed for its simple map design and incessant warnings to "mind the gap," it now carries over 1.3 billion passengers a year.

(Editing by Stephen Addison)