Amazon has again been operating secret flights carrying thousands of packages, this time in and out of the UK for the past six weeks as it trials setting up its own air freight business, according to a report in the UK’s The Evening Standard. Amazon has been quietly operating the flights since mid-November using chartered B737s to fly between Poland, the UK and Germany.

This latest report comes only months after it emerged that the e-commerce giant was quietly conducting tests of its own air freight service in the US code-named ‘Aerosmith’. The US-tests were being operated on Amazon’s behalf by Air Transport Services Group (ATSG) using four leased B767Fs.

The five-times a week flights operate from Katowice in Poland to Luton, East Midlands or Doncaster airports in the UK and then back to Poland via Kassel in Germany. The round trips link several of Amazon’s biggest fulfillment centres in Europe.

The report said Amazon is working with DB Schenker and is understood to be looking at extending the trials with further aircraft charters and taking in centres in Spain and Italy.