Sainsbury's and Co-op have joined Tesco in offering the best of their grocery deals to customers with a loyalty card.

Rumour has it Morrisons is to follow suit with a relaunch of its More card that’ll give holders member-only prices.

But we’re not talking about the odd item or two that’ll save you 10p if you can tap-in at the till – but hundreds and hundreds of products from food to toiletries where the difference numbers pounds not pennies.

Nescafe Gold Blend instant coffee for example - costing £4 for cardholders rather than £8.10 if you can’t show your Nectar card. Or Heinz baked beans costing 95p instead of £1.40 - but only if you can prove you’re a member at Sainsbury's.

It’s not even just confined to the larger stores, where you might accept you make a considered and planned trip and need to get that proof of membership sorted in advance.

A quick late night panic dash to a supermarket-branded convenience shop last week for packed lunch supplies – minus the loyalty card - saw me stung for juice cartons at 50p each compared to five for just over £1 had I my proof of an account.

Among the (many) things I find frustrating is not any longer being sure which of the two prices is actually reflective of an item's true cost?

Is the member-only deal genuinely heavily discounted to reward me for my loyal custom? Or are the standard / non-member prices massively over inflated to make a quick buck from unsuspecting shoppers yet to hand the supermarket their personal data?

I grant you – it worked once for me and my pricey fruit juice – but I won’t get caught there again. (In fact if you can’t judge from this column, a week on and I’m still not over it.) And not because of the money but the principle.

Don’t get me wrong, I’m fully aware supermarket bosses aren’t here to do me a favour. Times are tough and they’re fighting for our custom.

But forcing people to pay over the odds for essentials like washing powder, toilet roll or fresh fruit, simply because they didn’t join your private club shouldn’t be allowed.

And I doubt it makes them any more competitive either. Because with discounts on dozens of different items that change almost weekly – unless you’ve the time and energy to keep comparing your coffee or matching up the price of meat – you’re never actually comparing apples with apples, to excuse the pun.

Consumer campaigners at Which? have long been calling for people across the UK to have good clear access to cheaper food prices and budget ranges since food prices took-off like a rocket.

Yet the cost of food and supermarket pricing structures now seem more complicated than ever before.