Ultra Electronics surged on Thursday following a report the engineering and defence company could be a takeover target.
Markets blog Betaville, which cited people following the situation, said the identity of the bidder is unknown.
The company has been of interest to private equity firms in the past, Betaville noted.
Two years ago, Ultra held talks with its US-based joint venture partner, Sparton Corporation, about a combination of the businesses, which collaborate to make sonobuoys. However, the deal fell through after US officials said they wanted Ultra Elextronics and Sparton to compete for American navy contracts rather than merging.
At 1530 BST, the shares were up 5.7% at 2,250p.
