feel free to probe - I’m merely sharing what I was told by CS on the gold line a week ago in relation to my own 241 - that if I accepted an FTV for, I could then only use that value (avios) of the FTV (not the tax element) towards another cash booking, not to pay the taxes for reuse of the companion voucher. The taxes I paid would be put into an FTV, but that cash value could then not be used for taxes of a companion voucher.

In short: You pay cash (for taxes), plus Avios to use 241. You convert FTV into 2x FTV 1) is an FTV for the 241 avios value and 2) is an FTV for the cash you paid for taxes. You can use voucher 1 (avios) fairly easily but voucher 2 (taxe) cannot be used towards a new fare where you’d pay taxes only (so redemption/241 etc.) even though you used it to pay taxes originally - seems completely non sensical/unfair to me...

My intention in sharing this info is so people do not get caught out by accepting an FTV for a 241 only to find the voucher they have for the taxes they paid in cash is not valid against new taxes so they have to pay again (and use what was a taxes only voucher against a different new booking). BA seems keen on handing out FTVs like sweets so I’d hate anyone to get caught out...

Of course, as is always possible the agent I spoke to could have been making it up and you may have better luck with another!