According to one source the review is linked to the arrival of a new chief executive at the company in April. Martin Glenn was previously chief executive of Birds Eye and UK marketing director of PepsiCo.
The company counts Jaffa Cakes, Jacob’s crackers, Go Ahead!, Mini Cheddars and McVitie's among its brands.
Last year it slimmed down by selling its KP Snacks business, including Hula Hoops, to German firm Intersnack. Before the sale it recorded annual revenue of £1.3bn.
A United Biscuits spokesman said the company was reviewing PR arrangements for a number of brands within its portfolio for which activity has previously been handled in house.
'The process is being handled by The Observatory International and is expected to be completed by end of October 2013,' the spokesman added.
Among the agencies that have worked for the company recently is Mischief, which last year won a brief to ‘reignite passion’ for Jaffa Cakes.
Ad agency Grey London was last month awarded the company’s £10m advertising account, taking over from Publicis.
This story was updated at 11am on 3 September.