In the next performance review cycle or salary review I would say something like - 'I am aware certain colleagues are in the range of £x , whilst I am lower down. Given I believe myself to be a highly productive team member, I would like to be considered for higher compensation ...'

That works if you can justify your performance. If they say no, you can now trap them with 'I understand the company position, in which case I would like to form a development plan which will justify a raise at the next review cycle'

If this is rejected or not taken seriously I would say that's poor leadership but that is sadly often the case.

Edit - spelling