Paying for fuel O/T

Unless people already know, be warned. My wife fueled our car with £20 this morning. She has just checked our account and Sainsbury's have put pending every penny, basically emptying the account. She called Sainsbury's asking what was going on and was told 'this is common practice' if you pay at pump. The over payment can take up to 24 hrs to be re-embursed. This means if you have £1000 in the bank, pump pay for £50, you have loaned Sainsbury's £950 for 24hrs. Luckily we have some cash in the house. Just goes to prove 'cash is king'.