Is it permissible to take the sum of thirty pounds instead of the ten pounds allocated for attending the periodic meeting, given the inadequacy of the allocated amount in proportion to the importance of the meeting and those who attend it?

It is permissible to take the increase in the allowance if the committee head is authorized to do so by official bodies. Otherwise, it is not permissible for him to increase it, nor for you to take it, because he is entrusted with what is under his authority. Doing so would be assisting him in wrongdoing, and Allah Almighty says: (And cooperate in righteousness and piety, but do not cooperate in sin and aggression).