The competition, which is held on alternate years, was previously open to agencies with incomes of less than £20 million.
Work from agencies including Abbott Mead Vickers BBDO, Grey and JWT are among the entries, which will be judged by a panel including Lord Chadlington, the chief executive of Huntsworth, Andy Nairn, the planning director of Miles Calcraft Briginshaw Duffy, and Charlie Snow, the director of strategy at Delaney Lund Knox Warren.
BT, Shell, Nutella and the British Heart Foundation are among the brands that make up the 29 single and five joint entries.
Nairn said: "This year’s competition promises to be the most eclectic yet, with an unprecedented range of channels and disciplines represented – all proving that a relatively small budget can still be used to great effect."
The internet is the most popular medium in the competition, with 25 out of the 34 entries utilising digital elements. Press advertising was just behind online in the popularity stakes, being used in 22 of the entries, with TV advertising coming in a close third, with 21 entries.
The awards, sponsored by Thinkbox, will be presented at the Hurlingham Club on 9 November.