U.S.-based Coast, which owns around 2.8% of Blue Prism, had also objected to Vista's initial 1.09 billion pounds proposal made in September. Coast had instead backed a rival 1.16 billion pound possible offer last week from SS&C Technologies.

"Management has lost our trust in light of false and inconsistent narrative presented to investors - 1,250 pence is still far from fair value," said James Rasteh, founding partner of Coast Capital.

"We have evidence that many suitable PE firms were not contacted by (financial advisor) Qatalyst in this process," added Rasteh.

The increased cash offer of 1,250 pence per share from Bali Bidco Ltd, a firm indirectly owned by Vista, was announced late on Thursday. Blue Prism shares jumped up to 7.7% to 1,309 pence on Friday.

Blue Prism did not immediately respond to a Reuters request for comment.

Separately, the UK Takeover Panel has set SS&C a Dec. 2 deadline to make a firm offer for Blue Prism or walk away.

($1 = 0.7515 pounds)

(Reporting by Aby Jose Koilparambil in Bengaluru; Editing by Krishna Chandra Eluri)