Cna Re has been put up for sale by its Chicago parent company CNA Financial Corporation.
The organisation was downgraded a fortnight ago by ratings agency Standard & Poor's, following a weak operating performance. Its premium income had also been reduced from £561m in 1999 to £350m last year.
Now the London-based subsidiary is being sold, although its Lloyd's syndicate 1229 will continue operating.
CNA Re chief executive Stephen Riley said: “We are not exiting reinsurance in London. We are hoping to retain a significant proportion of our current business for future operations.
“We are selling the company, but not getting out of the business.”
He added US business would now only be written in the US, with international deals being insured in London and Zurich.
CNA Re was formed in 1976 and has 130 staff. It is one of the largest non-marine companies in the London Market.