Tanner, who was deputy head of Theresa May’s Policy Unit until the recent general election, has joined as Portland’s chief policy adviser. Trott, who worked as a special adviser to David Cameron, is joining as a partner in its corporate group and Number 10 deputy political director Hargrave returns to Portland as a corporate director.
Portland said Tanner, a senior researcher at the think tank Reform before working for the government, would advise clients on the policy priorities of the Conservative Government, including Brexit.
Trott, who was somewhat controversially made an MBE following her stint as head of strategic comms at Number 10 under David Cameron, previously worked in the Downing Street Policy Unit and as chief of staff to Cabinet Office minister Francis Maude.
Portland said Hargrave, who started his career at Portland in 2010, would "enhance the agency’s research and insight’s offer, amplifying its impact within the corporate group and act as a campaign strategist for clients". In addition to the Conservative Party's general election victory in 2015, he has worked on campaigns across Europe, Asia and the Caribbean.
Their appointments follow the promotion of Sam Ingleby to senior partner and head of Portland's 80-strong corporate group earlier this year.
London-based Portland, which was founded in 2001 by Tim Allan, a one-time senior adviser to former UK Prime Minister Tony Blair and director of comms at Sky, grew UK revenue 21 per cent to £27m in 2016, according to PRWeek Top 150 Consultancies table.
The agency - which also has offices in Washington DC, New York, Doha, Nairobi and Singapore – is majority owned by Omnicom. Last year it was revealed that the holding company is to take full ownership of Portland in the future.