LONDON, Jan 30 (Reuters) - U.S. Secretary of State Mike Pompeo warned on Thursday that trade talks with Britain would be contentious, particularly over agriculture, and he hoped that food safety would not be used as a ruse to protect certain industries.

Food standards, and the prospect that Britain would have to accept imports of chlorine-washed chicken from the United States in any trade deal between the two has become a symbol of what pro-EU Britons say will be a weak negotiating hand after Brexit.

Britain leaves the European Union on Friday to enter a transition period that runs until the end of this year, enabling it to open trade talks with the United States and others.

"There will be real contentious issues around agriculture..," Pompeo told LBC Radio during his visit to London, which he described as him acting as the "starting gun" for a new phase in cooperation between the two countries.

"Our ask will be as it has been in the other negotiations. We need to be open and honest about competitiveness. We need to make sure we don't use food safety as a ruse to try and protect a particular industry."

Pompeo said he hoped that by the late summer of this year the two sides would have made substantial progress in talks, before they move on to the most difficult issues. (Reporting by Kate Holton and Costas Pitas, editing by Estelle Shirbon)