Renewal season chaos means many London Market contracts will be finalised in late February.
Neil Golder, compliance director of brokers John Bannerman, said: "Underwriters do not know where they are. It is chaos."
He said the renewal season, which aims to have cover in place by 1 January, is extremely late as underwriters are not sure how much reinsurance is available.
"This leads to delays and uncertainty about the scope of cover," he explained.
Callum Stewart, managing director of non-marine reinsurance at Heath Lambert, said second-tier reinsurance also faced severe setbacks.
"The retrocession market was deliberately late in starting its season," he said.
"A lot of people will not know what final figures will be until the end of February."
A casualty underwriter with one of the top ten Lloyd's syndicates agreed policy details would not be completed for another two months.
He said: "I don't think I am going to have all my renewals until the end of February."
Insurers are now dictating larger deductibles and more stringent terms. Rates have also risen, with construction risks up by 150% to 200%.
One specialty products underwriter said: "It is going to be exclusive as to with whom we deal. There is such a large amount of business out there. We can name our price and pick and choose business."
Paul Tester, executive vice president and chief underwriting officer of Trenwick International, described the season as "the toughest any underwriter can remember".
He said: "Some of the following market have very clear ideas of what terms they expect to see and will hold out for them. January will be extremely busy."