More than 2,500 outlets across Bradford are still selling food containing a banned dye which can cause cancer, it was warned today.

A major health alert was issued after it was discovered that more than 400 food products had been contaminated with the illegal substance Sudan 1.

Government food experts have been working with national stores to remove the affected goods from sale. Bradford supermarket giant Morrisons has taken 44 product lines off its shelves.

But West Yorkshire Trading Standards has warned that around 2,400 independent stores, newsagents, take-aways and restaurants in the Bradford district are still selling the affected products without realising.

Now officers are planning to carry out on-the-spot checks at shops across the district to ensure food containing the dye is removed from sale.

And retailers who refuse to co-operate are being warned that they will be prosecuted.

Sudan 1 is an illegal red dye which was contained in chilli powder used in Crosse and Blackwell Worcester Sauce, produced by Premier Foods.

The sauce was then used as in ingredient in hundreds of products including foods made by Asda, Iceland, Heinz, Sainsburys, Marks & Spencer, Somerfield and Tesco.

West Yorkshire Trading Standards principal officer Trevor Gray said: "Our spot checks will be concentrating on smaller independent stores.

"A lot of the larger stores are taking instructions from their head offices but we will be looking at the smaller stores where there is not this chain of command. We think that there are around 12,500 retailers in West Yorkshire who will be stocking these products without realising and at least a fifth of these will be in Bradford."

Mr Gray said: "We cannot go to every single shop with a list that is seven pages long and check every single product, so we need stores to find out what they need to remove."

Retailers can find an updated list of products containing the illegal dye on www.food.gov.uk or contact Consumer Direct on 0845 4040506.

Mr Gray said: "We will be asking people for a voluntary withdrawal and we will not be taking legal action where people are selling products innocently without realising.

"But when it comes to the point where stores have been told not to stock products we expect them to comply and if they don't we will consider taking legal action.

"I have asked officers to report back to me but we don't expect to find any resistance."