After posting its biggest two-day percentage gain as US lawmakers agreed to a record $2 trillion stimulus package, the blue-chip index dropped 2.5pc with British American Tobacco, Ferguson and Prudential trading ex-dividend.
"The US stimulus news is probably the last piece of good news markets will get for a little bit, as attention now pivots back to the coronavirus curve and the scale of the economic damage," said Stephen Innes, a markets strategist at AxiCorp.
The FTSE 100 has fallen more than 25pc from its January peak, with further swings likely as data showed British retail sales failed to grow in February, even before shops shuttered due to the lockdown.
All eyes will be on the US jobless claims report, which many fear will be one of the worst in history.
"The data is going to look worse," said Alan Custis, head of U.K. equities at Lazard Asset Management. "But the shock effect is wearing off as the whole thing is morphing every week in terms of how investors are looking at it."
Meanwhile, the Bank of England and Britain's finance ministry were set to resume their coordinated stimulus drive, with Finance Minister Rishi Sunak laying out plans to support Britain's 5 million self-employed workers through the crisis.
Britain's financial regulators have already announced measures to give companies more time to publish results and banks more leeway for handling troubled loans.
Mall operator Intu Plc tumbled 13.7pc after saying it would seek debt waivers from its lenders and aid from the government's coronavirus support schemes as the health crisis hit rents.
Real estate firm British Land dropped 6.1pc.
Lender Non-Standard Finance slid about 10pc after it scrapped its dividend and said it has reduced its lending volumes across its divisions to preserve cash.
Aerospace engineer Senior Plc, however, was flat after saying it took cost-cutting actions to save cash, but suspended its 2020 outlook and scrapped dividend.