Sports Minister Hugh Robertson said he was as "confident as you possibly can be at this stage that we will deliver a safe and secure" London Marathon on Sunday.
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Passengers, including a pregnant woman, say they have been stranded since 4pm yesterday.
The boxer said it was the "least he could do" and even donated the £30,000 shorts he wore in his last fight against Devon Alexander.
By Sunday it should become drier with spells of winter sunshine but temperatures will still remain on the cool side.