Shoppers preparing for Pesach in Golders Green are resigned to an eye-watering till receipt. It is not uncommon for those entertaining during the festival to spend a four-figure amount on food and drink. And while expressing disbelief at the cost, observant shoppers feel they have no option but to pay up.

Among those spending £1,000 or more on Pesach provisions is Ruth, a north-west Londoner in her sixties, who has been stocking up at Kosher Kingdom. "I cannot understand why Pesach prices are so high," she says. "It doesn't make sense."

Ruth feels the festival has become a money-making exercise for manufacturers and retailers. "After Pesach, products are sold at half the price," she notes. "In Waitrose last year Pesach cakes cost £2 and then somehow went down to 50p."

Another shopper, mother-of-five Michal Wittenberg, 35, spends a similar sum on Pesach shopping for her family, but is more understanding of the increased prices.

"I buy everything kosher for Pesach, including washing-up liquid and toothpaste," she says. "If Pesach stuff needs extra supervision then no problem [about the extra cost]." Like many others, she makes savings by taking advantage of the offers on Pesach essentials at Tesco and other mainstream supermarkets.

The United Synagogue kashrut authority maintains that it is not the extra supervision at Pesach that hikes up prices.

Rabbi Jeremy Conway, director of the London Beth Din kashrut division, cites two key factors, firstly logistics. Factories that produce kosher for Pesach products may have to shut for a couple of days for Pesach cleaning, or it may be necessary to purchase extra production equipment for a separate Pesach production line, he points out.In addition, the alternative ingredients used in some Pesach foods are more expensive than those in the regular versions. "People assume that supervision and labelling push up the prices - this is not the case," Rabbi Conway says. "To be clear, London Beth Din supervision is provided at cost price as a service to the community. Where large quantities are produced, the cost per item is often negligible. It does not cost any more money for a product to be supervised over Passover than during the rest of the year."

Asked why chametz-free items such as teabags and sunflower oil also require a kosher-for-Pesach stamp, Rabbi Conway replies that common additives and processing aids used in everyday goods may contain chametz, thus everything must be checked.

By way of a history lesson, he says the supervision of tea dates back to the 18th century, when tea smugglers would mix tea leaves with fillers such as liquorice leaves and even animal dung. He does concede that in 2015, this kind of tampering is "highly unlikely". But he maintains: "The Passover label remains vital. Without it, how many people would realise that instant tea often contains chametz in the form of dextrose and malt?

"It is impossible for consumers to be confident of avoiding chametz unless all ingredients and production lines have been professionally investigated. Hence the beth din sanction."

Kosher-store bosses claim they are doing everything possible to be competitive on price.

At Hendon supermarket Tapuach, managing director Daniel Frohwein anticipates a 40 per cent increase in turnover on last Pesach. In the run-up to the festival, the majority of the store is given over to thousands of Pesach products. He sends out "secret shoppers" to his rivals and then compiles a price comparison chart.

"Whether rich or poor, we have to buy Pesach kosher food," he reasons. "It is abhorrent to try and profit from it unnecessarily."

Yossi Cohen of kosher supermarket chain B Kosher says rising demand has led to an increased festival range of almost 4,000 products. For example, responding to the needs of French Jews in London, he is importing more French items such as fine cheeses and yoghurts. He claims his stores match Tesco's prices - and can even be cheaper.

"Whatever they charge, they make money. We do lines at cost price."

A Tesco representative says there are 200-plus products in its range this year, with the biggest selections in its Borehamwood, Brent Cross and Cheetham Hill, Manchester, stores.

And for those living outside the main Jewish areas, Manchester-based Titanics expects to deliver as far afield as Cornwall and the Scottish Highlands.