Actuarial is harder to get into than Accounting in general. I say in general as it depends on the serviceline within Accounting. Something like audit is one of the more easier roles to get in to since it has one of the biggest intakes and comparatively low requirements. As someone mentioned, since you're talking about the Big 4, Accounting is naturally less competitive than Actuarial.
Also, this year, unlike previous years, one of the Big 4's declined the Soton Actuarial Society's careers fair invitation due to "a reduction in the number of vacancies we have in the Actuarial".