I've had recruiters do this (Explore LTD in London). The 'data collector' asked me my current salary and I refused to state it. She became very hostile saying

I've had recruiters do this (Explore LTD in London). The 'data collector' asked me my current salary and I refused to state it. She became very hostile saying "How are we meant to negotiate for you if you won't disclose what salary you are on?". I told her to let me negotiate my own salary.