The Military Wives choir single is now outselling the rest of the Top 20 combined, according to figures from the Official Charts Company.
They had sold 319,000 copies of their single, Wherever You Are, as of midnight on Tuesday with the other 19 acts combined selling slightly less.
The single is outselling nearest rival Cannonball by X Factor winners Little Mix by a margin of six to one and could hit the half-million mark by the end of the week.
The Military Wives were formed by Gareth Malone for BBC2 programme The Choir, which climaxed with the group performing at the Festival of Remembrance at the Royal Albert Hall.
Official Charts Company managing director Martin Talbot said: “This truly is an extraordinary result for Gareth and his choir – easily now the fastest selling record for years. They are extending their lead day-by-day and breaking records as they go.”
The choir received another boost with the Government agreeing to waive VAT on sales of the single which is on course to be Christmas number one this weekend.
The Treasury will give the money to charity in lieu of the tax taken from sales.
Choir member Sarah Wall said it was a ‘brilliant’ gesture.
Last month the Government agreed to a similar gesture for The X Factor’s charity single Wishing On A Star.
Proceeds from the single are being donated to the Royal British Legion and the Soldiers, Sailors, Airmen and Families Association.