More than a dozen charities working on the ground in Ukraine and neighbouring countries will benefit.
The Disasters Emergency Committee (DEC) has launched an appeal to raise urgent funds to help those forced to flee their homes amid escalating conflict.
Around 800,000 people have fled Ukraine in the last week and many more have been displaced inside the country due to intense fighting.
Inside Ukraine homes have been destroyed, essential infrastructure such as water supplies, hospitals and schools have been hit - with people being forced to hide in shelters and metro stations to stay safe.
As a result, hundreds of thousands of people are crossing borders into Poland, Romania, Hungary, Slovakia and Moldova, triggering a large-scale humanitarian crisis.
The UN estimates that 4million people could flee the country due to the conflict - the majority crossing the borders women and children.
DEC charities and their local partners are in Ukraine and across the border in the neighbouring countries, working to meet the immediate needs of all people fleeing with food, water, medical assistance, protection and trauma care.
The DEC brings together 15 leading aid charities at times of crisis overseas. Thirteen of these are responding in Ukraine and its neighbouring countries who have taken in refugees, including British Red Cross, ActionAid and Save the Children.
DEC chief executive Saleh Saeed said: “I could never have envisaged launching a humanitarian appeal in Europe in 2022. But tragically, that’s exactly where we find ourselves.
“Our members are working tirelessly with local partners to reach people in Ukraine swiftly as the brutal conflict turns lives upside down.
“Families, including many children, have been forced to leave everything they know behind to find safety and desperately need food, water and shelter.
“The DEC exists to mobilise the British public’s generosity and goodwill at times of crisis overseas, and this is one of those moments.”
Appeals to raise funds to support this work were broadcast on the BBC, ITV, Channel 4, Channel 5 and Sky on Thursday night following the evening news.
Andrew Morley, president and CEO of World Vision International, has just returned from Siret on the Romanian border with Ukraine and Albita on the Moldova border where he saw the relief operations in action.
He said: "We support children in countless crises across the world, but I have never seen a more heart-breaking situation. All the children I met were crossing the border in tears, with pain and fear in their eyes. They were lost and scared.
“They need the basics – simple, practical help. Our staff have been present in this area for decades and there on the ground to deliver it – but we need financial support to do this.”
Every pound donated by the UK public will be matched by the UK government through its Aid Match scheme up to the value of £20m.
This support will double the impact of the public’s own donations and will ensure that charities working on the ground can reach those in urgent need.
Prime Minister Boris Johnson announced the UK Aid Match in PMQs in the House of Commons this week.
Foreign Secretary, Liz Truss said “The UK stands with people fleeing this terrible conflict and we are working with our humanitarian partners to provide for those in need in Ukraine and the wider region in their hour of need.
“Through the DEC Ukraine Humanitarian Appeal, we will match, pound for pound, up to £20m of donations from the Great British public, ensuring vital support reaches communities in desperate need of help.”