The new series of The X Factor may just be one night old, but the show is already under fire after it emerged that Philippine girl group 4th Power are already seasoned professionals.

Viewers saw the four sisters from Manila – Almira, 27, Irene, 25, Mylene, 23, Celina, 19 – perform the Jessie J track 'Bang Bang' on Saturday''s show with the judges enthusiastically giving the girl group for yeses.

It has emerged, however, that the foursome are actually professional musicians and have appeared on and won a series of talent contests already - and even have records available to buy on Amazon.

They also go under the names MICA and The Gollayan Sisters, and have over two million views on YouTube.

In 2012, they won the top-rated Philippine's X Factor-style TV talent show It's Showtime and made the final eight last year on Korean singing contest Superstar K.

An X Factor source told the Sunday People: "Producers were well aware who the girls were before they arrived in front of the judges – so it was no surprise that they were ­fantastic on the show.

"Executives looked at everything they had done before and discussed them at length before making the decision to invite them back and make them a big part of the launch show. Obviously they were exactly what had been expected.

The show insists that the judges were not aware of the sisters past.

"But the judges had not been told what was coming, to ensure their ­reaction was as strong and completely natural as it could be."