Well, 1 point per full £4 on the Tesco credit card doesn't sound great to me.
£100 spend on the Tesco credit card - assuming it is in multiples of £4 = just 25 points = 80 BA Miles at the old rate (or 60 at the current rate).
£100 spend on the BA AmEx Premium Plus card - assuming in full pounds - produces 150 BA Miles. Similar spend on the regular BA Amex produces 100 BA Miles. Both beat the Tesco earnings.
As Raffles points out, the Tesco rate is poor and is useful if you want to use it at an outlet that doesn't take AmEx, though there are far better MasterCard and Visa cards.
It would take a lot to convince me that the current card is any use other than as Raffles advises. I'm glad I have the old card offering 1 point per full £ at Tesco stores, tesco.com and Tesco Travel, and 1 per full £2 elsewhere including Tesco petrol.
These calculations ignore the points earned on the Tesco clubcard, which are additional.