Grassroots aid destined for Ukraine is spending day stuck in lorries at the port of Dover because of Brexitborder checks.
Charity workers say that five tonnes of donations are still in the UK because of confusion over paperwork.
Britain's exit from the EU single market and customs union caused a dramatic rise in bureaucracy for imports and exports between Britain and the EU.
The red tape is now making it harder to send supplies to help in the wake of the Russian invasion, where the UN says need is "growing at an alarming pace".
According to the UN's humanitarian assistance office as of Monday there are now 12 million people in need in the country and a $1 billion (£760 million) shortfall in funding.
Over the weekend UN Secretary-General Antonio Guterres called for a cease fire to allow the passage of life-saving humanitarian aid to those encircled by Russian forces in the country.
But some aid sent from the UK is getting stuck even closer to home because of Brexit delays.
Agnieszka Lokaj, who runs the Lewisham Polish Centre in south London, told the PoliticsHome website that despite mounting donations, "we are not exporting".
"I don’t want to send drivers to the border where they will be stuck for several days. It doesn’t make sense to spend so much time and money dealing with the bureaucracy," she said.
Last month lorry queues of up to six miles (10km) into the port of Dover we're recorded by Highways England – from the Roundhill Tunnel to the Western Heights Roundabout
HMRC, which oversees customs and other regulatory checks on goods crossing the border, recommended that people donate to the UN's Disasters Emergency Committee as the best way of helping the country.
Since 1 January 2022 lorries have had to use the Goods Vehicle Movement System (GVMS) to get through customs at the port. The new governemnt IT system deals with customs, transit and security declarations needed to cross the Channel.
Before this year goods could be exported and paperwork dealt with afterwards, but this grace period has now elapsed. Even lorries with the right paperwork – which is complicated and often filled in by specialists rather than the lorry drivers themselves, are taking 15 minutes to clear the border. Those without the right paperwork or where an error has been made are not allowed through.
A Government spokesperson said: “People and businesses across the UK have already responded with immense generosity, donating millions of pounds to support those forced to flee their homes as a result of the war in Ukraine.
“Government advice remains that the best way to help the Ukrainian people is to donate money through the Disasters Emergency Committee or other trusted charities.
“However, we appreciate that people and businesses may still wish to donate aid directly to the region and we are exploring further ways to support this. Anyone requiring advice can contact the free-to-use Export Support Service (ESS)”.
