Mumbai: Shiv Sena chief Uddhav Thackeray on Monday said there would be an official announcement on poll alliance  in the next two days. However, he made it clear that after thorough deliberations, the formula for exchanging seats between his party and the BJP will be finalised. "Some things are being worked out. In the next couple of days, the official announcement of the BJP and the Sena contesting the elections will be made," Thackeray told reporters after NCP MLA Avdhut Tatkare, nephew of Raigad Lok Sabha MP Sunil Tatkare, joined the Sena at his suburban residence. Thackeray, while sharing a stage with the PM at a function in Mumbai on Saturday, said the saffron alliance was "atal" (inevitable) and it will return to power once again.