The largest peace march since before the Iraq invasion is expected to descend upon Downing Street today demanding that Tony Blair calls for an unconditional ceasefire in the Middle East.

In a powerful demonstration of the groundswell of opinion across Britain, as many as 100,000 people are predicted to take to the streets around Parliament Square.

As Mr Blair was this week forced to concede that even members of his cabinet had "doubts" over his handling of the situation, protesters will deliver children's shoes to his London home to represent those whose lives have been lost in the 24-day conflict.

A letter bearing 40,000 signatures will also be handed in, calling on Mr Blair to work towards ending the "bloodshed and destruction unfolding daily".

Among many high-profile figures supporting today's march is the designer Katharine Hamnett, whose political T-shirts began a trend of sartorial protest more than 20 years ago. She has designed a special limited edition proclaiming simply: "Unconditional Ceasefire Now."

The Stop the War Coalition, which has organised the demonstration at "breakneck speed" in just seven days, said staff had been stunned by the strength of the response. Other organisers of the protest include the British Muslim Initiative, CND, the Palestine Solidarity Campaign and Lebanese community associations.