The move means Frank has wrestled the lion's share of Persil work away from rivals Lexis PR and The Red Consultancy.
The first task on the agency's agenda is the current launch of Persil brand small&mighty - a double-concentrated laundry detergent.
It is to be positioned as ‘the biggest innovation in the laundry category for ten years'.
Three other unnamed ‘major projects' will also be overseen by the agency this year, with Frank taking charge of Persil's press office.
Industry insiders estimate the work to be worth at least £300,000 a year, but neither Frank nor Unilever would comment on fees.
Frank joint MD Frankie Cory (neé Burstin) will lead the account.
Frank's win comes after the agency handled two projects for Persil last year.
It helped out on the ‘Be my coach' campaign, which encouraged kids and their parents to get outside and exercise together. It also handled publicity for Persil Non-Bio's tie-in with Warner Bros' Happy Feet film (PRWeek, 27 October 2006).
Fluffy penguin toys were given away with packs of Persil Non-Bio around the film's 8 December release in a bid to appeal to mothers.
Last year Red worked on the ‘Dirt is good: The Persil 33 things to do before you're 10' campaign. Lexis had handled the core Persil campaign since 2005.
Both agencies are still retained as part of the sprawling Unilever consumer roster that covers the multinational's vast cosmetics, detergent and grocery ranges.
Persil is approaching its 100-year anniversary (it was introduced in 1909) and claims to be used by more people in the UK than any other detergent brand. It also claims that nearly a third of the UK's 17 million daily washes include a Persil-branded product.
One of Persil's main rivals is Procter & Gamble-owned Ariel, which gains publicity each summer through its associations with the Lawn Tennis Association and the Wimbledon Championships.