The activity led to speculation that a predator was building up a position prior to launching a takeover bid for the company.
One analyst said that mystery surrounded the share buyers. He said: "Swan Hill doesn't know and we don't know who is buying." He added that the only recourse open to the management was to convince shareholders that they ought to hold onto their stakes.
Swan Hill shares were trading at 81p on Tuesday – 4p higher than the previous Friday. However, the analyst said this undervalued the company and left it open to a bid. Its net asset value per share is about £1.25.
He said: "A potential buyer might think there was more to get out of the company.
"It is asset rich but cash poor, which makes it vulnerable." John Theakston, chief executive of Swan Hill, said he doubted the flurry of activity signalled a takeover bid.
He pointed to the small shift in the price of shares as proof that the company was not being stalked by a predator.
He said: "We're trying to find out [who is buying the shares] but I doubt someone is building a new position.
"I suspect it was a transfer between institutions, or between an institution's funds, because the price did not move that much." Housebuilder Linden, which owns about 3% of Swan Hill, denied suggestions it was buying up more of the company.
Chief executive Philip Davies said that although Linden had no interest in acquiring the company it would be attractive to others.
"It's undervalued and so it's not out of the question that it might be a target from either a listed housebuilder or an unlisted one." The activity came as Swan Hill announced results for the year to 31 December, posting pre-tax profit of £2.3m, down from £4m in 1999. Turnover dropped £11m to £59.6m.
Theakston said the company had successfully completed its strategy of switching from a property and construction company to a pure housebuilder.
Swan Hill had sold 90% of its property portfolio and settled the last construction contract, Brook House, at a loss of £2.4m.