As part of the deal, the percentage of Admiral's business underwritten by Great Lakes will be reduced over the next five years.
Currently, Great Lakes is responsible for underwriting 65 per cent of Admiral's car insurance business and this is due to be reduced to 40 per cent by 2011.
Admiral also said that it had signed reinsurance contracts with Swiss Re and Partner Re, with both companies set to reinsure percentages of its car insurance premiums.
Swiss Re will cover ten per cent of premiums from 2007, although this will reduce to five per cent by 2011. Partner Re will cover 7.5 per cent for 2007 and 2008.
The contracts can be cancelled with two years notice, Admiral added.