The time taken by the Financial Services Authority (FSA) to give financial services firms permission to expand has hit a record 97 days.
This figure has trebled from 25 days in 2008 and increased 10% in the past year, law firm Reynolds Porter Chamberlain (RPC) says.
Firms must apply for a "variation of permission" in order to expand via a new line of business, new regulated activity or a new class of customer.
Jonathan Davies, regulatory partner at RPC, said: "The FSA's checking process is becoming more laborious than ever before.
"The financial services sector is a key employer and vital generator of tax revenue.
"If the FSA's intrusive approach is applied indiscriminately and prevents well run, stable businesses from expanding, it damages competition and both the consumer and the economy will suffer."
He added the FSA is required by law to be aware of the effects it has on competition within financial services, and that it has a duty to avoid creating unnecessary barriers to business expansion.
The FSA aims to process most applications for variations of permission within three months.
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