This week it emerged that the hotel group had dumped retained agency The Hogarth Partnership from the brief and drafted in rival Financial Dynamics, following advice from investment bank Merrill Lynch.
Thistle CEO Ian Burke was unavailable for comment, but it is understood Merrill Lynch wanted to appoint advisers it had previously worked with.
The bank refused to comment.
The move does not affect Hogarth's status as Thistle's retained financial PR agency
Thistle's decision also follows complaints made by the takeover panel on earlier press coverage of the bid, which resulted in the group issuing a clarifying statement last month.
Hogarth founding partner Nick Denton confirmed FD's appointment does not affect their seven-year retained relationship with Thistle: 'Merrill Lynch requested that another financial PR firm comes in who they have worked with on other hostile bids, but we will continue our retained relationship with Thistle.'
Thistle this week stepped up its defence strategy as Singapore investment firm BIL released its second offer document.