The Chancellor has been challenged over his vow to crack down on single-use plastics – three months after addressing the issue in his Budget.
The Labour chair of the Environmental Audit Committee, Mary Creagh, called on Philip Hammond for answers after publishing a letter to him on Thursday.
It comes after Mr Hammond said in November he would "investigate how the tax system and charges on single-use plastic items can reduce waste".
Ms Creagh spoke of the "public concern around the impact of plastic pollution on our environment" and put it to the minister that "it is now three months since that announcement".
The letter demands clarity on when any possible consultation will take place, how long it could run for and whether it would be the Treasury or Defra who would carry it out.
"Pollution from single use plastic packaging is choking our oceans and devastating marine wildlife," said Ms Creagh.
"Three months ago ministers promised to look at using the tax system reduce the use of throwaway plastics, but still have not published a call for evidence.
"The Government has talked the talk on plastics pollution, but it has been too slow to walk the walk."
In his Budget, Chancellor Philip Hammond described plastic waste as a "scourge" and said he was looking into a single-use plastic tax.
In January, Theresa May set out plans to get rid of avoidable plastic waste within 25 years.
More from environment
The Prime Minister said she wanted to "make ours the first generation to leave the natural environment in a better state than we found it" as she unveiled her Environmental Plan.
She said plastic was "one of the great environmental scourges of our time".