You can try. I would think that once fuel contamination is proven they will meet the claim for the repairs, but you may be in dispute for the travel costs you are claiming. I think £1125 is "reasonable" for your use of your other car as replacement because you tried to "mitigate" the cost by using your own vehicle instead of hiring another van for which the bill could have been £3000 - £4000. Good luck. Even if you get the £4500 repair cost, you may have to go to small claims court for the travel expenses.