Overrunning engineering works brought fresh misery to commuters using Britain's busiest rail station on the day it was supposed to open for business as normal following major works.

Rail users reported services into London Waterloo being delayed or cancelled altogether, as nearly a month's worth of disruption caused by the transport hub's £800 million overhaul lurched into Tuesday.

Stations including Queenstown Road, Earlsfield and Norbiton were also closed.

A Network Rail spokesman said: "The upgrades taking place at Waterloo station are some of the biggest and most complex engineering projects ever undertaken on the railway.

"We are entering the final stages of that programme and are preparing the railway and station for trains and passengers.

"During the process of testing the complex signalling, we identified an issue in this safety-critical system which we are working to resolve.

"This will take some time to fix and a small number of early passenger trains may be delayed as a result.

"We are working hard to minimise delays to passengers, but safely is our number one priority."

Network Rail said it expected disruption to be resolved by noon.

Responding to the announcement on social media, Dave Vasse tweeted: "Predictable & embarrassing that Waterloo should be a mess today after 8 months of advertising 28th completion date."

Chloe Grover wrote: "Cancellations, delays, no info. Great welcome back to Waterloo."

Another, Sam Maher, added: "1st train of day & a guard has 'bit of bad news'. Waterloo still mashed. Wish I'd placed that 'no way be finished 28th' bet now."

Announcing that the station had "fully reopened" despite the problems, Network Rail route managing director Becky Lumlock said: "The work we have completed in three-and-a-half weeks this August will benefit passengers for decades to come. The longer platforms will create space for longer trains, making journeys more comfortable for passengers, particularly at the busiest times of day.

"Over the next 16 months we'll turn our attention to the final stages of the redevelopment of the former international terminal. We'll be working behind the scenes so that we can, by the end of next year, permanently bring the five extra platforms back into use for what will become a modern, high- frequency commuter terminal fit for the 21st century.

"I'd like to personally thank passengers for their patience over the last few weeks, and apologise for disruption to their journeys this morning.

"I'd also like to pay tribute to our 1,000 strong army of engineers and track workers who have delivered such an enormous project."