Report by Granada Reports correspondent Mel Barham
The Mines Advisory Group will work with local people and Ukrainian authorities to dispose of mines and other munitions.
They will also educate communities about the dangers and how they can stay safe.
The charity has teamed up with non-profit Ukrainian Deminers Association, with an immediate focus on educating vulnerable communities about landmines and UXO (unexplained ordnance).
Mines Advisory Group employs 5,700 staff in 27 countries and has significant expertise in clearance in post-conflict countries like Iraq and Syria.
The organisation says towns, villages and cities in Ukraine have been affected by landmines, alongside rural areas.
The team says there is evidence of contamination by cluster munitions, as well as improvised explosive devices (IEDs) and other explosives in Bucha, Irpin, Andriivka and Borodyanka, close to the capital Kyiv.
MAG International Policy and Partnerships Director Josephine Dresner, who led the assessment mission, said: "The overall extent of contamination in Ukraine is now so extensive that it will almost certainly require several hundred million pounds and decades of difficult work to clear.
"That is why it so important to work in close and constructive cooperation with Ukrainian organisations so that we are aiding the Ukrainians to build their own capabilities, resources and capacity to deliver a long-term, sustainable approach to the challenges ahead."
Staff from the charity have been meeting with people whose lives have been affected by the conflict, many having lost their homes and, in some cases, close family members.
At one point during the initial assessment mission, the team had to warn family members returning not to return to their home because of a suspected IED at the property.
Data experts at MAG have also been using satellite imagery to assess which areas have been worst affected by explosive weapons.
Survey and clearance work is expected to begin later this year.
Ukraine's Deputy Interior Minister Yevhen Yenin said that about 300,000 km² of Ukrainian territory - an area larger than the UK - is suspected of having been contaminated by explosive ordnance since 24 February.
MAG says an estimated 2 million people were already at risk of landmines and explosive remnants of war in the east of Ukraine prior to the Russian invasion earlier this year, a result of the conflict in 2014.
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