The Charity Commission has spent nearly £1.5m on consultants and agency staff since the start of this year, latest figures show.
The bulk of this went towards the implementation of a new case management system, the regulator said.
Transparency data on the commisson's spending is released on a monthly basis.
The regulator was allocated £27.3m from central government in the year to the end of March 2021 and will receive an additional £1m in 2021/22.
The latest data shows expenditure that includes individual invoices, grant payments, expense payments and other transactions that are worth more than £25,000.
It shows that between 1 January and 31 May, the regulator has spent almost £1.5m on “consultancies” and “agency staff” among eight different companies including the services firms Serco, PwC and Capita.
PwC’s work includes “performance and planning” and “development and tasking”.
About £800,000 has been spent with a company called Sopra Steria, a Paris-based consulting and digital services company, which is advising the commission on what it describes as an “IT roadmap”.
The commission said this spending was for a new case management system.
A UK company called Embridge Consulting has also been paid more than £270,000 for services related to the IT roadmap.
The regulator said the payments to PwC were for "time-limited projects" around its business continuity plans, and Serco helped place reminder calls to charities that missed reporting deadlines.
Nearly £60,000 has been spent with a company called Behavioural Insights, known unofficially as the “Nudge Unit”, which aims to use theory and data on public behaviour to inform policy and improve public services.
It was originally set up within the Cabinet Office to apply nudge theory, which proposes positive reinforcement and indirect suggestions as ways to influence the behaviour and decision-making of groups or individuals, across government. It became a limited company in 2014.
More than £42,000 was spent with media agency Manning Gottlieb in April on “SRO communication & policy projects”, the spending data shows.
The outsourcing company Capita provided agency staff in April and May at a cost of about £103,000.
On average, the regulator said that agency recruitment cost the same as employing a permanent member of staff.
A commission spokesperson said: "Lockdown and the necessary switch to homeworking for our staff has resulted in savings for the commission across this and last year, for example on travel costs.
"We have invested this saving in accelerating some of our planned improvements, such as to customer services, as well as increased support for our existing workforce as they continue to advise, assist and regulate charities during the challenges of the pandemic.
"As there has been continued uncertainty over how long this period of cost savings will last, we have mostly chosen to use agency staff as they are quicker to bring in and it allows us to be flexible in response to the funding available.
"All payments to outside agencies are as a result of strict competitive procurement processes that meet government standards."