Trading standards officials are investigating complaints that some tickets for Robbie Williams concerts have not been delivered.
Robbie Williams: His Leeds concerts have been hit by problems
The tickets were bought from agency Harley Street Ticket Brokers in London, which has reportedly ceased trading.
Westminster City Council staff are now making efforts to see if tickets for the gigs - including two in Leeds this weekend - can be recovered.
A spokeswoman said it had received a "steady stream of complaints".
"These complaints, along with being told the company had ceased trading, compelled us to launch an investigation," she added.
"Westminster's trading standards team are doing everything in their power to get to the bottom of what is going on with this ticket agency."
It is the latest of a number of problems that have hit the singer's concerts in Leeds.
A row erupted after 11 schools were closed by the council, who feared for the safety of children amidst the 90,000 fans heading to the gig.
Meanwhile other fans had problems after two bags of tickets were lost.
However the tickets are now set to arrive before the first of the concerts.
The former Take That star has also confirmed he will play his first gig in China, in Shanghai on 4 November.