Budget Group's affinity business Junction has beaten top insurers to supply Marks & Spencer's (M&S) motor policies.
M&S Financial Services head of insurance Peter Longstaff said: "Budget had beaten very stiff competition, many of them direct companies."
But he could not say which companies were rejected, because of a confidentiality agreement.
"We chose Budget because of its excellent claims service and competitive panel,"he said.
The panel will include Norwich Union (NU), AXA and Churchill.
Budget chief executive Peter Winslow said: "This contract win shows that we have a very strong business proposition for the affinity insurance market."
The policy, available via the M&S website or by telephone, includes integrated UK breakdown from the RAC, repair cover, free key care cover for chargecard holders and up to £10,000 for personal injury. Other perks include provision of courtesy cars in the event of a claim. And personal effects include up to £500 for goods bought at M&S.
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M&S Financial Services already offers household through NU, travel, pet insurance through AXA and wedding cover underwritten by Ecclesiastical.