M&S Cameron dress was made specially for her

An "off-the-peg" Marks and Spencer dress worn by Samantha Cameron during the Conservative Party conference had to be specially made for her as a one-off.

David Cameron's wife was praised for her decision to wear the £65 grey and cream polka-dot dress during the conference.

Choosing the modestly-priced outfit was seen as a sign of sensitivity to the hardships facing the nation during the recession.

The dress, launched by Marks & Spencer earlier this year, was so popular that it quickly sold out.

But Mrs Cameron was taken by the design and efforts were made to secure her a copy even though the dress was no longer available.

London-based designer Amanda Marshall Ltd, which dreamed up the dress, had been dropped as supplier to the retailer earlier in the year.

But Marks & Spencer went back to ask if the company could whip up a one-off sample for Mrs Cameron.

The cost of making the sample was around £150 - more than double the sale price of the dress.

Amanda Marshall Ltd agreed in the hope it would result in the company gaining another contract with the retail giant. But the designer said it received no acknowledgement of the "good will gift" from Marks & Spencer. An Amanda Marshall Ltd source said: "They did this out of good will, hoping that if they helped Marks & Spencer out, they would probably get another contract with them."

A spokeswoman for Marks & Spencer said Mrs Cameron never asked for the dress but had told Sir Stuart Rose, chairman of the company, that she liked the garment when they met during a function.

Mrs Cameron did pay for the dress when it was presented to her, she added. A statement from the retailer read: "Marks & Spencer commissioned a former supplier, Amanda Marshall Ltd, to produce this dress specifically for us."