London shares fell sharply today as the prospect of tighter Covid-19 restrictions over Christmas leads to more turbulence for European markets. The rapid spread of the Omicron variant and its impact on the global economic outlook has also weighed on oil, with Brent crude trading more than 3% lower at just above $71 a barrel.The main corporate developments involved FTSE 100 boardroom changes after mining giant Rio Tinto appointed Dominic Barton as its new chairman and GlaxoSmithKline named former Tesco boss Sir Dave Lewis as chair-designate of its consumer healthcare division. The FTSE 100 index has dived 1.7% in the latest sell-off linked to the fast-spreading Omicron variant. Demand fears meant commodity stocks were at the forefront of the slump as Anglo American, BP and Antofagasta all fell by 3% or more. The prospect of tighter travel restrictions, including bans on UK visitors to Europe, meant British Airways owner IAG fell 5% and Rolls-Royce dropped 4%. Events business Informa was the biggest top flight faller at 6% lower.The UK-focused FTSE 250 index was down 2%, taking it back to the level last seen in the summer. Upper Crust business SSP and WHSmith both fell more than 5%. Oil prices have fallen sharply and investors face another turbulent session as European markets react to the tightening of Covid-19 restrictions ahead of Christmas. The rapid spread of the Omicron variant has resulted in a fresh lockdown in the Netherlands and other countries are considering their response, including potential bans on UK travelers. Brent crude fell more than 3% to $71.17 a barrel today as traders responded to the travel ban impact on jet fuel sales.