Translation of the letter from the Rabbis of London:
Since a Concert is being planned to take place soon in our city, that is a means to break down the tznius and purity of our community, and the Gedolei Hador have seen that this brings a foreign culture into the tents of Yaakov, and have expressed strong opposition to this, and have forbidden to participate in these concerts. Therefore we join in their proclamation, and all those who care for their souls must stay far away from this and ensure that the members of their families do not go to these places. And all those who listen to us will be guarded from all danger.
* * *
HaRav Michel Yehuda Lefkowitz, Zichron Meir Bnei Brak
13th Iyar, 5764.
We have heard that some people are organizing in your area a "Chassidic pop concert." It is already well known that this is not in the spirit of the Torah and its observers, and all the gedolei hador have already given their opinion that it is forbidden to go there or to participate in their performances, since this causes Rachmono litzlan to lower and destroy the chinuch that the teachers have given to the young people, both to boys and girls, and even has influence on their parents.
And as it is taught in the gemora Avodoh Zora, 27b on the posuk, "Whoever breaks through a fence will be bitten by a snake," that this is referring to heresy that influences people to be drawn after it. Such is the case of the pop concert that is being organized, that all the devotion that has been invested in chinuch will be destroyed, chas vesholom!
We can also learn important halochos from this gemora how much a person is obligated to distance himself from these matters that draw his heart astray, whether by means of listening or seeing or through the influence of street layabouts. And even if they give an excuse that the proceeds are going to charity, and that there will be complete separation by a mechitzoh between the men and women, it is still included in the warning to stay far away from such things.
May all those who listen to our words merit to a pleasant and joyful life,
Michel Yehuda Lefkowitz
It has already been well known and publicized for many years that these pop concerts, that are very far from the fear of G- d and from tznius are forbidden. I therefore join with the above words.
Waiting for the salvation of Hashem,
Shmuel Halevi Wosner
We also join in the above statement,