Squires, 30, collapsed and died during the final mile of the London Marathon on April 22.

Tests are being carried out to determine whether the heart condition had contributed to her sudden death that day.

A friend told The Sun newspaper that Squires had been diagnosed with the condition, adding: “It didn’t stop her keeping fit. It might have made a lesser person take a back seat. But Claire just got on with it.”

Squires was running the 26.2-mile course to raise money in honour of her brother, Grant, who died of a drug overdose in 2001 aged just 25.

She had raised a total of £500 when she began the run, but donations have poured in since her death, so that the current total stands at £1.1 million.

High-profile donors to the cause include Sir Richard Branson and Alesha Dixon.

Pictures: Getty