Joseph Lewis, a Bahamas-based investor, has acquired 12 million shares in two days, lifting his stake to 25.32 per cent. He declared a 4 million purchase on Tuesday and yesterday said he had picked up another 8 million.
The group's shares rose 4p to 213p, coppers below their year's high.
It is thought Mr Lewis has been stalking Christies for more than a year. His buying first attracted attention in the summer when, through his investment vehicle Abel, he said he had 16 per cent.
The auctioneers are familiar with large overseas shareholders. Japanese interests have featured on the group's share register and Sweden's Wallenberg family once had 7.5 per cent. ADT, the controversial car auction and security group created by Michael Ashcroft which is now based in Bermuda, once had a 24 per cent interest. To cut debts it was forced to sell - losing an estimated pounds 80m.
Mr Lewis could be banking on a Christies trading upsurge. Profits last year fell pounds 2.5m to pounds 16.4m. The market is looking for pounds 20m this year and more than pounds 25m next.
But the speed of his build-up is more likely to herald a more predatory interest. A fine art collector and racehorse breeder he is said to speculate in the currency markets.
He is not noted as a corporate player, although he has been involved with quoted London companies, including a leisure group.
The stock market had a roller-coaster session swinging from a 17.2-points fall to an 8.6-gain and ending 1.4 down at 3,662.8. New York's failure to hold the 5,200 level, touched in early trading, ensured a late rally petered out.
Government stocks offered a little inspiration, despite a poor reception to the auction. They scored gains of over pounds 1, encouraged by US Treasuries.
The Footsie upheaval was announced after the market closed. Anticipating its departure, Inchcape slumped 19p to 217p but Midlands Electricity, helped along by its proposed special dividend and share split, took its removal calmly, gaining 18p to 983p.
British Petroleum followed the Government's share sale with a 7p gain to 524p with Smith Barney, the US investment house, and NatWest Securities backing the shares. NatWest was also keen on Shell, up 5.5p to 820.5p.
BT continued to decline, worried by the proposed Oftel price curbs and increasing competition. The shares fell 6p to 352p, lowest for three years.
Bass jumped 26p to 695p following its results; Ladbroke, despite the failure of the rumoured Bass bid to materialise, gained 2.5p to 160p. Rank Organisation's encouraging trading statement lifted the shares 16p to 425p.
Berisford gained 17p to 190p following its profits recovery, but NFC lost 10p to 139p after its profit collapse. Vymura, the wallcovering group, slumped 35p to 104p on a profits warning.
Williams Holdings gained 7p to 321p with SBC Warburg moving from hold to buy.
Standard Chartered fell 16p to 588p (after 580.5p) as stories, subsequently denied, circulated that it planned to close its money market and derivatives operations.
Megalomedia, the new Saatchi vehicle, continued its heady progress, gaining a further 11p at 94p. The shares were relisted on AIM on Tuesday at 33p.
Another AIM newcomer had a spectacular start. Flomerics, a software group, was placed at 130p and closed at 205p. Profits of around pounds 400,000 are forecast for this year against pounds 406,700. Pet City, with 35 superstores selling pet requirements, is due to make its AIM debut today and some suggest another heady performance. The shares were placed at 300p and an opening price of more than 350p is expected.
T&N was actively traded ahead of an expected US judgment over asbestos claims. The shares shaded to 120p.
Cluff Resources, involved in bid talks, had another eventful session, jumping 14p to 92p with stories going the rounds a deal had been agreed. The shares have become a speculators' delight.
Recently they fell back sharply as rumours the talks had been abandoned went the rounds.
Newcomer Wilmington, once part of the Maxwell empire, made an impressive start, closing at 61p against the 50p issue price.
Psion, the hand-held computer group, continued to suffer from the loss of NatWest Securities as one of its two market-makers. The shares tumbled 70p to 765p.