The proposal, submitted for approval last month, will mean the loss of at least 100 beds.
It comes as the review of London's health care, commissioned by Health Secretary Frank Dobson last summer, arrives on ministers' desks. The review, by a five-strong panel chaired by Professor Leslie Turnberg, former president of the Royal College of Physicians, is believed to call for a halt to bed closures in London.
The panel is also believed to be critical of the plan to close St Bartholomew's hospital and move its services to the Royal London hospital at Whitechapel, but has found it difficult to devise a cheaper two-site solution.
The London review is also likely to criticise Guy's and St Thomas' plans on the grounds of cost, estimated at pounds 114m by the trust (half to be provided by the hospitals' special trustees) but nearer pounds 200m by the Save Guy's Campaign, and over the loss of beds, estimated at 100 by the trust but at 300 by the campaign.
The latest proposal involves transferring the Evelina children's hospital, which occupies six floors of New Guy's Houseto a new 232-bed women and children's hospital to be built on the St Thomas' site. The move follows directly from the decison to close Guy's accident and emergency department in 1999. "You have to have the women and children's hospital where the A & E department is," a spokes-man said.
The business plan says that following the move, expected by 2003, New Guy's House, which currently provides 400 beds, "will be mothballed, thereby providing future flexibility".
Tim Matthews, chief executive of Guy's and St Thomas', said: "If the Save Guy's Campaign believes there is a better plan that is both clinically coherent and costs less they should present it."