British insurer Standard Life said on Wednesday it was considering the possibility of making a cash and shares offer for rival Resolution, which has already agreed to merge with Friends Provident.
Britain's fifth-largest insurer said a move on its smaller rival Resolution could include the disposal of certain assets, but gave no details.
A spokesman for the group declined to comment on the disposals, price or timing of a possible offer.
Resolution shares jumped on the news to trade up 5.5 percent at 1345 GMT at 691 pence, valuing the group at 4.7 billion pounds ($9.5 billion). Standard Life shares were up 3 percent at 282.25 pence, off an earlier high of 301.25.
The move by Standard Life throws fresh doubt on Resolution's planned merger with Friends -- already threatened by another competitor, Pearl, which has built up a key shareholding and said it is considering its options.
Resolution, which announced the all-share nil-premium merger with Friends in July, said immediately after the Standard Life announcement on Wednesday that it was going ahead with the Friends deal -- but confirmed it would consider alternatives if they offered more value and equal certainty.
Pearl separately said it was still considering all its options but declined to comment on whether it would work with its rival on a joint offer or consider buying some Resolution assets if they were disposed of after a deal.
We rule nothing in and nothing out, a Pearl spokesman said.