An ongoing trial showed that only one out of 1,673 participants reported adverse reactions to rapeseed oil, according to the regulator. It added that it was still waiting for “clinical confirmation” that this was an allergic response.

The Anaphylaxis Campaign, a British charity specialising in supporting those with severe allergic reactions, said “although allergic reactions to rapeseed oil are almost unheard of… accurate food labelling is of the utmost importance to food allergic consumers, and we will continue to monitor the situation extremely closely.”

The British Retail Consortium said that retailers were looking to change product labels as soon as possible. 

Where sunflower oil was a key ingredient that had or was being replaced, firms could ink jet the words ‘rapeseed oil’ on the label. It added that retailers took their responsibilities “very seriously”.

Emily Miles, chief executive of the FSA, said that “retaining consumer trust remains an absolute priority”.

She added: “We have looked at the immediate food safety risk of substituting sunflower oil with refined rapeseed oil – particularly to people with a food allergy – and it is very low. We know allergic reactions to rapeseed oil are very rare and – if they do occur – are mild.”

The FSA separately published a rapid risk assessment into the substitution of sunflower oil with refined rapeseed oil.

It said: “Based on the lack of reports of adverse reactions to refined rapeseed oil in the UK population, and lack of evidence of severe illness or deaths, we estimate the frequency of allergic reactions to be very low and the severity of illness to be negligible.”

Earlier this month food and drink manufacturers started calling for a loosening of the rules.

Kate Halliwell, chief scientific officer at the Food and Drink Federation (FDF), said: “UK manufacturers are working hard to ensure food remains on the shelves amid intense global supply chain pressures.

“We welcome the decision that companies can alter their labels to reflect the current lack of availability of sunflower oil, but it is troubling that it has taken two weeks to reach this point.”

She warned that other short-term substitutions of ingredients may arise.

The FDF is working with the Government to ensure there is a “rapid process” in place to allow this.