Half of existing benefit claimants in Waverley waiting to move to Universal Credit are yet to be transferred, new figures show.
It comes as an anti-poverty charity warned hundreds of thousands of people across Britain have lost support as they move from legacy benefits to Universal Credit.
Universal Credit was introduced in 2013 to replace several existing benefits, in a bid to simplify the benefit system.
People receiving Jobseekers’ Allowance, Child Tax Credit and Housing Benefit among others are gradually being transferred onto Universal Credit, with the Department for Work and Pension resuming the issuing of migration notices in July 2022 following the coronavirus pandemic.
But payments to many receiving these older benefits were stopped completely, rather than moving to the new system.
DWP figures show around 650 migration notices had been submitted to legacy benefit and tax credit claimants in Waverley between July 2022 and March.
Of these notices, approximately 80 (12%) cases were closed, resulting in someone losing their benefits.
But Turn2Us said people could be missed as the DWP aims to transfer almost all legacy claimants and all tax credit recipients to Universal Credit by 2024-25.
In Waverley, roughly 51% of people sent a migration notice during this period remained on legacy benefits as of March 31, meaning they could yet be stripped of their support.
Of the 460 households who received a migration notice, around 63% had been contacted in the last three months, which is the timeframe the DWP gives people to migrate to Universal Credit.
The DWP initially estimated 3% of households would lose their benefits when transferring to Universal Credit. It later adjusted this to 26% of tax credit-only households and 4% of those receiving legacy benefits.
Across Britain, 22% of existing claimants had been stripped of their benefits between July 2022 and March.
Turn2Us said it is "deeply concerned the process of managed migration has seen thousands of people drop off benefits altogether".
Claire Atchia McMaster, director of income and external affairs at the charity, said many claiming legacy benefits have complex needs and may lack digital access to manage their support.
She added: "It is vital the process of contacting and supporting these people is not rushed, ensuring they are given adequate time, accessible information and personalised support to move over to Universal Credit.
"Disruption to benefits payments alongside the five-week wait for Universal Credit could cause serious harm to their finances and lives."
Those who did not voluntarily transfer to Universal Credit and receive less than their previous benefit support are provided with financial protection.
Some 166,860 households across Great Britain received transactional protection during the same period, a top-up designed to aid people's migration to a lower income – including around 100 in Waverley.
A DWP spokesperson said: "The majority of tax credit claimants have successfully moved to Universal Credit.
"Our statistics show that only 30 people logged complaints while over half a million households had been invited to move to Universal Credit by the end of March.
"There is a range of support available to help people move, including extensions for those who need extra support."