Berkshire Hathaway International Insurance (BHII), trading as Holdsure and Enterprise Motor Policies, has severed some of its administration deals with Link Insurance Services.
BHII previously tied all its customer data into Link's computers, but decided to create its own systems when the sale of Link by its parent, Kiln, was announced.
Link was initially to be sold to Ockham, but the deal fell through after the 11 September terrorist attacks. Now Rubicon will buy it.
BHII will now do its own administration, including policy documentation, in-house.
Underwriting manager Stewart Jenkinson said: "We realised that all our data was tied to Link's machines.
"It was a vulnerable position for any insurer to be in, to be dependent on another, especially when one is being sold."
Brokers are being warned they must contact BHII to renew policies for 2002, as they will not renew automatically. Policies will automatically lapse from renewal if instructions have not been received within 28 days of the renewal date.
The insurer's claims will continue to be handled by Link.
BHII bought the renewal book of syndicate 892 at Lloyd's, Holdure Motor Policies, when it ceased underwriting in 1998.