In the past month, Mr Lewis, through his Abel investment vehicle, has paid more than £14m for almost 6 per cent of the auction house. He has used the small London broker Hargreave Hale to buy shares and has notified the company of his interest. The stockmarket has yet to acknowledge his attentions: Christie's shares have fallen by 9p to 158p in the last four weeks.
Although no talks have taken place between the parties, Christie's will be anxious to establish what the motive of Mr Lewis is.
Little is known about the 57-year-old, who keeps houses in London, Berkshire and the Bahamas. He is said to be a heavy investor in the currency markets, where he takes large speculative positions. He is believed to have interests in bloodstock, through his association with JP McManus, an Irish bookmaker, and John Magnier, a substantial investor in the industry. He also collects art and recently paid more than $2m (£1.3m) for a painting at a Sotheby's sale in New York.
He was a director of a health food company based in London called Health Nut. The company has never filed accounts, but in company records he gives his address as Lewis House, Lyford Quay, Nassau, Bahamas.
Christie's refused to comment about the stake, and Mr Lewis could not be contacted last night.
It is not the first time the auction house has attracted the attentions of predatory investors. The Australian financier, the late Robert Holmes a Court, held a 7.3 per cent stake before selling to Yasumichi Morishita, a moneylender with a conviction forillegal share dealings. Then in 1990, Michael Ashcroft, the controversial chairman of ADT, the group with interests ranging from car auctions to burglar alarms, bought a 22 per cent stake. He increased his stake rapidly from less than 5 per cent to morethan 20 per cent but was seen off by the Christie's board, then chaired by Lord Carrington, when ADT became embroiled in litigation with one of its large shareholders, Laidlaw.
Mr Ashcroft made an £80m loss when he sold his holding.
Observers say Mr Lewis could be buying Christie's stock in the hope that it will recover, rather than as a precursor to a bid. The company is considered to be a difficult target for a hostile bid, because it could upset staff, on whose relationship with buyers and sellers the business hinges.
The share price, which has fallen from 250p since the beginning of the year, has not responded to the 15 per cent leap in half-year profits and a 19 per cent increase in turnover announced recently.
Sales of the art collections of the late Viscountess Rothermere and Barbra Streisand helped to push profits up, as did fire sales by Lloyd's names needing to raise funds.
However, the group did not increase its dividend, and warned that competitive pressure was growing.
Announcing the results, Christopher Davidge, the chief executive, said: "There are a lot of wealthy people around who want to buy the very best and we are seeing rising demand, in particular from Hong Kong, Singapore and even China."
The company has invested heavily in its network of offices and has devoted substantial resources to developing its presence in east Asia and Latin America. Earlier this year, it became the first mainstream auction house to open an office in Shanghai.
Christie's has never quite closed the prestige gap with Sotheby's, which now belongs to the American Alfred Taubman, but it has scored a number of coups.
The most celebrated was its sale of Van Gogh's "Sunflowers" to the Australian tycoon Alan Bond for more than £20m.
The group's finance director, Peter Blythe, said earlier this year that he did not expect the art market to return to the overblown days of the 1980s, but that it was improving steadily nevertheless.Reuse content