Meanwhile, rival Associated Newspapers has accused distributors of thelondonpaper of forcing copies on customers or dumping piles in places like buses, diluting the purity of the young affluent audience it sells advertising against.
Steve Auckland, head of Associated Newspapers' free newspaper division, said: "We have a lot of experience with Metro and we have always aimed for 400,000 (for the London Lite).
"There are no plans to increase circulation at this stage. We don't want to go down the route of dumping copies. We try to individually merchandise copies to consumers."
In December, audited circulation for thelondonpaper was 410,898. However, the average daily circulation last week was 493,069, according to the publisher.
General manager Ian Clark said that, last week, circulation hit the half million mark several times.
Since thelondonpaper's launch in September, News International had been offering a 33% "launch discount" to agencies, which it hoped to remove on 1 January this year.
The newspaper's rate card is based on a circulation of 400,000.
However, it said at launch it would only charge for 80% of any circulation rises above that, excepting a 10% normal allowance for daily distribution fluctuation.
"The strategy was to get to 400,000 comfortably and then after six months push that figure higher," Clark said last week.
He added: "We are confident that we can easily hand out the extra 100,000 copies. As soon as we demonstrate an uplift in circulation, we can stop offering the launch discounts to advertisers."
London Lite's circulation remains at around 400,000. The newspaper's December ABC figure was 400,692. Associated Newspapers' Auckland said: "We have a rate card with which we are comfortable. If they feel they need to add value to their offering, then that's fine."
The additional 100,000 copies will add to the three tonnes of extra waste that is created each day in Westminster by free newspapers.