In the summer, the company organized fan zones where people could watch the Champions League final.

Last year, LS Events won a place on an elite list of ‘approved suppliers’ who are allowed to organize outdoor events on behalf of the Mayor of London.

There are only six companies on the approved list and they bid against each other or can sometimes potentially bid unopposed for contracts when they come up.

City Hall says this list has been drawn up by officers from the Greater London Authority using normal processes and an open tender.

When the tickets to see Taylor Swift were first offered by LS Events in June, City Hall says they were “discussed with officials who had nothing to do with the procurement process”.

They were not accepted by the mayor until the night before the concert and “no one who received a ticket was involved in the procurement process”.

The spokesman added: “The mayor has no conflict of interest. The mayor has no involvement in the procurement process.”

Neil Garratt, leader of the Tories on the London Assembly, said: “Awarding a company a contract after accepting the offer of lavish hospitality during the tender process would be an outrageous breach of ethics.

“It’s expressly prohibited in the GLA hospitality rules, I can’t believe people in the mayor’s office didn’t know that.

“Was the late declaration and failure to name the company just an accident, or was it an attempt to cover up serious wrongdoing?”

City Hall has so far refused to explain why the mayor declared the gift 10 days late.

But it meant the details were not entered into City Hall records for the public and media to see at the height of the “freebies” controversy that engulfed the Labor leadership in the first three weeks of September.