Any harm in telling recruiter what other roles I am interviewing for?

Is it risky to disclose the exact company/role/ref number? If they are from a different agency (to the one representing me for that other role), are there ways for (the unscrupulous part of) them to scupper my efforts?

I'd never disclose any such information beyond the really generic - "it's a fintech firm around York" for instance, should be more than enough (if you even want to give that much info.) There's no advantage for you in them knowing the specifics, and they could potentially do one of a few bad things with that info:

• They may introduce themselves to the company and say they know you, then try to claim commission if you're hired there;
• They may also be hired by that company for that role (you've just found them via another means), and therefore they could explicitly recommend to the company that they don't hire you for whatever reason in order to get their commission;
• Unscrupulous, but they may have contacts they can use informally or otherwise to try to make sure you don't get that job, or you're lowballed on an offer (so you end up rejecting it.)

If they know that you're generically interviewing elsewhere, that could potentially be an advantage in that they want to prioritise getting you good places to make sure they get their commission (and likewise they're therefore more likely to negotiate a higher offer.)

They can / will be persistent, because it's definitely in their advantage to gauge the position you're interviewing for - so you just need to be insistent back and say something like "Just as I wouldn't disclose any opportunities you may provide me with, I'm going to be unable to give any more specific information on the role you're asking about."

If they keep pushing, just say "I'm afraid if this information is needed to progress, then it's probably better we don't carry on beyond this point - thank you for your time" or similar. They'll almost certainly change their tune at that point, and if not, go find a recruiter who will.