"My previous salary is irrelevant and

I'm happy to take an offer at market rate (in line with my experience)." could be your first answer. 

As a rule of thumb, I wouldn’t mind telling a recruitment agency my target salary range if they insist because their revenue of is often related to the salary offered. As a result, it might be reasonable to speculate that they would “sell” you at the dearest price. Or, they just want to fill a section of their database to facilitate their job search in case some CEO jobs get popped up.

However, to answer this question to a hiring company, I would try to resist it as stubbornly as I could since I had no idea about their budget. To tell them first, I might risk to scare them away or to get lower paid.