A group of insurers and Lloyd’s syndicates have launched legal proceedings against BP to block the oil and gas giant claiming on a $US700 million ($848 million) accident policy.

BP is attempting to limit the cost of the Gulf of Mexico oil spill by claiming coverage on a policy held by rig operator Transocean.

However, 38 Lloyd’s syndicates and a handful of insurers have filed a claim in a Houston court alleging the group has “no additional insured obligation to BP”.

The group claims Transocean’s policy only covers damage to the rig and liabilities stemming from pollution above ground.

BP uses captive insurance, and has no external insurance in place for the accident.

“Because liabilities BP face for pollution emanating from BP’s well are from below the surface and from BP’s well, those liabilities are not within the scope of the additional insured protection,” the court filing states.

The syndicates named in the filing represent nearly half of Lloyd’s.

Total insured losses from the accident were placed at $US1.4 billion ($1.7 billion) by the Insurance Information Institute. However, more recent figures by UBS estimate insured losses at $US12 billion ($14.5 billion). Swiss Re calculates insured losses will come to $US3.5 billion ($4.25 billion).

BP’s clean-up costs so far total $US760 million. But this figure excludes 14,000 unresolved claims. BP and Transocean also face more than 130 lawsuits.

The disaster has also prompted a hike in offshore drilling insurance costs. MarketScout, an electronic insurance exchange, says the cost to insure offshore drilling in the Gulf of Mexico has risen 15% in a month.