John McDonnell said that the slowdown in growth in the last quarter from the previous quarter showed a "slow erosion" of the British economy.
The shadow chancellor said: "Manufacturing fell back in this quarter and that's an indication of the slowdown that's happened in our economy overall.
"We've always said that we never expected an immediate crisis. What we were worried about was a slow erosion of our economy if we don't get certainty and security for the future."
In a speech on Thursday, Mr McDonnell said that the Government had to be "clear about its objectives and its approach to prevent uncertainty".
More top news
He said people have handed over thousands of pounds in good faith, only to find the advert has nothing to do with Mr Lewis or his company.
The memorial service will be attended by Prince Harry and Meghan Markle.
David Browning admits manslaughter by diminished responsibility but denies murder.