Businesses have been experiencing "significant delays" to their research and development (R&D) tax credit claims in recent months.
R&D relief is available to companies that work on innovative projects in science and technology, with the aim of making an advance in their field.
HMRC aims to pay out on R&D tax credit claims within 28 days, but the Chartered Institute of Taxation (CIOT) said processing times are taking much longer.
Responding to the CIOT, the Revenue said it has taken action to reduce processing delays to both R&D tax credits and RDEC claims.
Additional staff have been brought in to process both R&D claims, in the hope of being up to date with all unprocessed claims by 30 September 2019.
A spokesperson for the CIOT said:
"We understand it is not possible for HMRC to guarantee achieving this as it will depend on a number of factors, including how soon HMRC can get people trained to undertake the work, any complications that emerge from the claims already submitted, and also how much new work comes in.
"But we welcome HMRC's assurance that being up to date by 30 September is its aim and ambition."
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